WO2008152506A2 - A method and a device for depositing or removing a layer on/from a workpiece, an analysis method and device for analysing an expected layer thickness, a method for setting up a database for such an analysis method or device, as well as such a database - Google Patents

A method and a device for depositing or removing a layer on/from a workpiece, an analysis method and device for analysing an expected layer thickness, a method for setting up a database for such an analysis method or device, as well as such a database Download PDF

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Publication number
WO2008152506A2
WO2008152506A2 PCT/IB2008/001905 IB2008001905W WO2008152506A2 WO 2008152506 A2 WO2008152506 A2 WO 2008152506A2 IB 2008001905 W IB2008001905 W IB 2008001905W WO 2008152506 A2 WO2008152506 A2 WO 2008152506A2
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WO
WIPO (PCT)
Prior art keywords
specific element
workpiece
layer thickness
expected
database
Prior art date
Application number
PCT/IB2008/001905
Other languages
French (fr)
Other versions
WO2008152506A3 (en
Inventor
Bart Juul Wihelmina Van Den Bossche
Original Assignee
Elsyca N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Elsyca N.V. filed Critical Elsyca N.V.
Publication of WO2008152506A2 publication Critical patent/WO2008152506A2/en
Publication of WO2008152506A3 publication Critical patent/WO2008152506A3/en

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/22—Secondary treatment of printed circuits
    • H05K3/24—Reinforcing the conductive pattern
    • H05K3/241—Reinforcing the conductive pattern characterised by the electroplating method; means therefor, e.g. baths or apparatus
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D21/00—Processes for servicing or operating cells for electrolytic coating
    • C25D21/12—Process control or regulation
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/02—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding
    • H05K3/06—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding the conductive material being removed chemically or electrolytically, e.g. by photo-etch process
    • H05K3/07—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding the conductive material being removed chemically or electrolytically, e.g. by photo-etch process being removed electrolytically
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
    • H05K2203/01—Tools for processing; Objects used during processing
    • H05K2203/0104—Tools for processing; Objects used during processing for patterning or coating
    • H05K2203/0117—Pattern shaped electrode used for patterning, e.g. plating or etching

Definitions

  • the invention relates to a method for depositing or removing a layer on/from a workpiece, wherein an electrolyte is present between said workpiece and at least one counter electrode and a potential difference is applied between said workpiece and said counter electrode for depositing or removing said layer, which deposition or removal is preceded by an analysis phase, in which an expected layer thickness of the layer to be deposited or removed is calculated on the basis of data from a database.
  • the invention also relates to a device for depositing or removing a layer on/from a workpiece, which device comprises a tank in which, in use, at least an electrolyte and the workpiece are present, which device further comprises at least one counter electrode and a power or voltage source for applying a potential difference between the workpiece and the counter electrode for depositing or removing the layer on/from the workpiece in use, which deposition or removal process is preceded by an analysis phase, in which an expected layer thickness of the layer to be deposited or removed is calculated on the basis of data from a database.
  • the invention also relates to an analysis method for analysing an expected layer thickness of the layer to be deposited on or removed from a workpiece, wherein an electrolyte is present between said workpiece and at least one counter electrode and a potential difference is applied between said workpiece and said counter electrode for depositing or removing said layer.
  • the invention further relates to a device for analysing of an expected layer thickness of the layer to be deposited or one or removed from a workpiece, wherein an electrolyte is present between said workpiece and at least one counter electrode and a potential difference is applied between said workpiece and said counter electrode for depositing or removing said layer.
  • the invention also relates to a method for setting up a database suitable for use in such an analysis method or device.
  • the invention further relates to such a database.
  • a printed circuit board (PCB) surface is divided into a number of grid elements for an arithmetic model wherein an average current density during the deposition or removal of the layer and an active surface area fraction, being the ratio between the electrically conductive area in the grid element that is to be actively treated and the total geometric area of the grid element, is calculated for each specific element. Subsequently, it is determined on the basis of the active surface area fraction ⁇ and the calculated current density whether or not the expected layer thickness is acceptable.
  • the grid elements into which the workpiece is divided are relatively large (in the order of mm/cm), so that the total number of regions is limited and the required computer time is also relatively limited.
  • a drawback of the known method is that in this way an analysis of the layer thickness to be realised at so-called specific elements is not obtained.
  • a specific element is a relatively small element, usually having a three-dimensional topography, in the workpiece, such as a through hole or a blind hole having a diameter of 0.05-2 mm.
  • the object of the invention is to provide a method for depositing or removing a layer on/from a workpiece which makes it possible to realise a desired layer thickness on the workpiece, and in particular at a specific element.
  • a specific element may for example also be a local elevation or an internal cavity having a small radius of curvature, for example an electrical conductor on an integrated circuit. Such conductors may have a very small width of up to 30 nm. This object is accomplished with the method according to the invention in that
  • an expected potential distribution in the electrolyte near the workpiece is calculated during the analysis phase, whilst an expected local potential difference between the electrolyte and the workpiece is calculated at least at a specific element on the workpiece,
  • At least the layer thickness at at least one historic specific element stored in the database is retrieved in said database, of which historic specific element at least the local potential difference at least substantially corresponds to the expected local potential difference of the specific element provided on the workpiece, which layer thickness is regarded as the expected layer thickness at the specific element on the workpiece,
  • the expected layer thickness is compared to a desired layer thickness at the specific element, - whereupon, if the difference between the expected layer thickness and the desired layer thickness exceeds a predetermined value, measures are taken to change the expected local potential difference at the specific element so that the layer thickness to be realised and the desired layer thickness substantially correspond.
  • the expected layer thickness at the specific element i.e. in and around the specific element, will be comparatively large. In that case there is even a risk that the layer deposited at the specific element will fill the specific element entirely, which is undesirable in many applications, such as a through hole or a blind hole in a printed circuit board.
  • Other applications, such as conductors on an integrated circuit on the other hand require that the specific element be filled entirely, without internal cavity and without any overgrowth over the photoresist layer.
  • the active surface area fraction ⁇ at the specific element is comparatively high, there is a risk that the layer to be deposited at the specific element will be too thin or even absent altogether around or in the specific element.
  • the realised layer thickness substantially corresponds to the desired layer thickness over the entire workpiece, and in particular at the specific element.
  • the predetermined value of the layer thickness may be a single value, but it may also be a range of values, in which case the expected layer thickness must be within said range.
  • the expected layer thickness must be greater than a minimum desired layer thickness and smaller than a maximum desired layer thickness.
  • Mouton's theoretical model does not make use of a database in which information is stored regarding previously processed workpieces, and in particular regarding realised layer thicknesses at specific elements, at the location of which the local potential difference during the deposition of the layer substantially corresponds to an expected local potential difference at a specific element of the workpiece now to be processed.
  • the historic specific element with the substantially corresponding local potential difference may be an element of a type and category other than the specific element of the workpiece now to be processed.
  • An advantage of the use of such a database is amongst others that as more information regarding realised layer thicknesses near specific elements with specific local potential differences and if desired other boundary conditions is stored in the database, the expected layer thickness will corresponds better with the layer thickness actually te be realised near the specific element.
  • One embodiment of the method according to the invention is characterised in that said measures comprise the placement of at least one co- electrode, an additional counter electrode or an isolation shield near the specific element, so that a local potential difference is obtained, which will result in a desired layer thickness at the specific element.
  • the local potential difference V-U By placing a counter electrode near the specific element, the local potential difference V-U, wherein U is the local potential in the electrolyte and V is the potential of electrically conductive local part of the workpiece, will become more negative (deposition of material) or more positive (removal of material). This can also be realised by placing an isolation shield near the specific element.
  • the invention further comprises a device suitable for carrying out the above-described method, which device is characterised in that the device
  • - is connected to an arithmetic unit for calculating an expected potential distribution in the electrolyte near the workpiece and an expected local potential difference between the electrolyte and the workpiece at at least one specific element on the workpiece, - is connected to a database in which at least layer thicknesses at historic specific elements and as well as the local potential differences during the deposition or removal of the layer are stored,
  • - is connected to a retrieval unit for retrieving in the database the layer thickness of at least one specific element of which at least the local potential difference at least substantially corresponds to the expected local potential difference near the specific element on the workpiece, which layer thickness is regarded as the expected layer thickness at the specific element on the workpiece,
  • a difference unit for determining the difference between the expected layer thickness and the desired layer thickness at the specific element, as well as for indicating that if the difference exceeds a predetermined value, measures will be taken in the device to change the expected local potential difference at the specific element until the expected layer thickness and the desired layer thickness substantially correspond.
  • the object of the invention is to provide an analysis method which makes it possible to indicate prior to the deposition or removal of a layer on/from a workpiece whether a desired layer thickness at a specific element can be realised or that additional measures are required.
  • an expected potential distribution in the electrolyte near the workpiece is calculated, whilst an expected local potential difference between the electrolyte and the workpiece is calculated at least at a specific element on the workpiece,
  • At least the layer thickness at at least one historic specific element stored in a database is retrieved in said database, of which historic specific element at least the local potential difference at least substantially corresponds to the expected local potential difference of the specific element provided on the workpiece, which layer thickness is regarded as the expected layer thickness at the specific element on the workpiece,
  • the potential distribution over the workpiece can be calculated on a macro scale over the workpiece in a simple manner, for which purpose only a limited computer capacity needs to be available, if the workpiece is divided into comparatively large grid elements, each having their own surface area fraction ⁇ .
  • the presence of the specific element can be left out of consideration in the determination of the potential distribution U over the workpiece, hardly affects the calculated expected potential distribution U, on account of the very small share of the specific element in the active surface area fraction ⁇ in a grid element.
  • the active surface area fraction ⁇ can be calculated as follows:
  • a act is the area of a grid element that is available for a Faraday reaction
  • a sup is the total area of the predetermined grid element
  • ⁇ is the electrical conductivity of the electrolyte, I n i s t h e i n w a rd ve ct o r , perpendicular to the wall.
  • the above precondition can be adapted by means of the local active surface area fraction ⁇ :
  • the expected layer thickness d after a predetermined processing time ⁇ t, on the electrode surface, but not at the specific elements, therefore, can then be determined as follows:
  • M is the atomic weight of the metal to be deposited or removed
  • p is the specific weight of the metal
  • z is the number of electrons exchanged in the metal reaction
  • F is Faraday's constant.
  • the expected local potential difference V-U at the specific element can be obtained in a simple manner on the basis of the calculated potential distribution U over the entire workpiece.
  • Stored in the database are data of previously produced workpieces and the specific elements thereof, wherein the data relating to a historic specific element stored in the database comprise at least the local potential difference during the treatment of said historic specific element, as well as data regarding the realised layer thickness at said historic specific element.
  • a historic specific element is retrieved whose local potential difference substantially corresponds to the expected local potential difference of the specific element on the workpiece yet to be treated.
  • the layer thickness of the historic specific element stored in the database is then regarded as the expected layer thickness of the specific element on the workpiece and compared to the desired layer thickness. When relatively large differences are detected, measures will be taken to adjust the expected local potential difference.
  • the local potential difference V-LJ is a suitable and relevant value for determining whether the layer thickness to be realised can indeed be realised at the location of a specific element.
  • j n / ⁇ is also a suitable measure thereof, because a univocal, continuous and monotonous function f brings the two quantities into connection.
  • the expected layer thickness can be accurately determined in a simple manner on the basis of the local potential difference V-U and the active surface area fraction ⁇ .
  • the specific element comprises a through hole or a blind hole, which hole has a length and a diameter at least substantially the same as the length and the diameter of the specific element to be retrieved in the database.
  • One embodiment of the analysis method according to the invention is characterised in that, in the case of a specific element comprising a through hole, also the pressure difference in the electrolyte on either side of said hole is calculated, wherein substantially the same pressure difference prevailed at the historic specific element to be retrieved in the database upon electrolytic deposition or removal of the layer at said historic specific element.
  • Yet another embodiment of the analysis method according to the invention is characterised in that the local hydrodynamic boundary layer thickness in the electrolyte at the specific element is calculated, wherein substantially the same local hydrodynamic boundary layer thickness was found to be present at the historic specific element to be retrieved in the database upon deposition or removal of the layer at said historic specific element.
  • the local hydrodynamic boundary layer thickness affects the layer thickness to be realised.
  • Said hydrodynamic boundary layer thickness can simply be calculated on a macro scale for the entire workpiece and be determined in a simple manner at the location of the specific element on the workpiece. Comparing the specific element on the workpiece to be treated with a historic specific element which exhibited substantially the same local hydrodynamic boundary layer thickness upon deposition or removal of the layer at said historic specific element, makes it possible to realise a more precise determination of the expected layer thickness at the historic specific element on the workpiece.
  • Yet another embodiment of the analysis method according to the invention is characterised in that the historic specific element to be retrieved in the database was treated in electrolyte substantially the same as the electrolyte in which the workpiece is to be treated. It has been found that the electrolyte is a determining factor as regards the layer thickness to be realised at the specific element.
  • Yet another embodiment of the analysis method according to the invention is characterised in that if the expected layer thickness is smaller than the desired layer thickness at the specific element, the local potential difference is adjusted by taking measures at least comprising the placement of an additional counter electrode at the specific element.
  • Said counter electrode preferably has a pin-shaped structure for influencing the potential difference V-U as locally as possible near the specific element whilst influencing the flow of the electrolyte past the workpiece as little as possible.
  • the counter electrode realises an adjusted local potential difference V-U near the specific element, so that the expected layer thickness will be greater.
  • Yet another embodiment of the analysis method according to the invention is characterised in that if the expected layer thickness is greater than the desired layer thickness at the specific element, the local potential difference is adjusted by taking measures at least comprising the placement of a co-electrode at the specific element, which co-electrode drains part of the current between the counter electrode and the workpiece.
  • Such a co-electrode reduces the current between the workpiece and the counter electrode at the location of the specific element and also reduces the layer thickness.
  • the invention further relates to a device, which device comprises - an arithmetic unit for calculating an expected potential distribution in the electrolyte near the workpiece and an expected local potential difference between the electrolyte and the workpiece at at least one specific element on the workpiece,
  • a retrieval unit for retrieving in the database the layer thickness of at least one specific element of which at least the local potential difference at least substantially corresponds to the expected local potential difference at the specific element on the workpiece, which layer thickness is regarded as the expected layer thickness at the specific element on the workpiece,
  • a difference unit for determining the difference between the expected layer thickness and the desired layer thickness at the specific element, as well as for indicating that if the difference exceeds a predetermined value, measures must be taken to change the expected local potential difference at the specific element until the expected layer thickness and the desired layer thickness substantially correspond.
  • the expected layer thickness can be determined in a simple manner by determining the local potential difference and comparing the specific element with similar specific elements in the database, after which measures may be taken, if desired, to change the local potential difference.
  • the invention further relates to a method for setting up a database suitable for use with an analysis method and/or device according to the invention.
  • the method according to the invention is characterised in that a layer is deposited on a workpiece or removed from the workpiece, wherein an electrolyte is present between said workpiece and at least one counter electrode and a potential difference is applied between said workpiece and said counter electrode for depositing or removing said layer, after which at least one specific element on the workpiece is selected and subsequently a section of the specific element is made, the data of which section are stored in the database, whilst furthermore the expected potential distribution in the electrolyte near the workpiece as well as an expected local potential difference between the electrolyte and the workpiece at the location of the specific element are calculated, whilst at least the expected local potential difference is stored in the database and linked to the data relating to said section.
  • the workpiece is a printed circuit board provided with dozens, possibly hundreds or even thousands of specific elements, data regarding many specific elements can be collected by producing one or a few printed circuit boards.
  • the database composed by means of the method can be set up by one company and subsequently be made available to various companies that want to use the analysis method and device according to the invention.
  • Figure 1 is a diagram for setting up a database, which database is suitable for use in the analysis method and device according to the invention
  • FIG. 2 is a diagram showing the analysis method according to the invention.
  • Figure 3 is a time flow diagram of a bipolar pulsed current signal
  • Figures 4a-4d are top plan views of a printed circuit board layout, isolines of active surface area fraction ⁇ , isolines of a deposited layer thickness distribution and isolines of a potential distribution in the electrolyte along the printed circuit board;
  • Figure 5 is a perspective view of a device suitable for carrying out the method according to the invention.
  • the database 1 shown in figure 1 is intended for use in an analysis method for analysing a workpiece, such as a printed circuit board, for example, on which a layer is to be deposited.
  • a workpiece such as a printed circuit board, for example, on which a layer is to be deposited.
  • the workpiece and a counter electrode are placed in a tank (cell) containing an electrolyte, and a potential difference is applied between the workpiece and the counter electrode. Said potential difference causes current to flow from the counter electrode through the electrolyte to the workpiece, and an electrochemical reaction will take place at the interface between the electrolyte and the workpiece, as a result of which a metal layer will be deposited on the workpiece.
  • Such a manner of depositing layers is known per se, inter alia from the aforesaid US patent, and will not be explained in more detail herein, therefore.
  • a number of printed circuit boards are produced and tested for setting up a database suitable for use in analysing layer thicknesses on a printed circuit board.
  • a printed circuit board is selected and the layout of the circuit to be patterned thereon is stored in a computer.
  • global process conditions are stored in a computer, such as the current I, the time ⁇ t during which the current is applied between the workpiece and the counter electrode, the flow rate of the electrolyte in the tank, the air agitation, the type of electrolyte, the processing temperature, etc. This takes place during S2.
  • step S4 a number of specific elements are selected (step S4), which specific elements are through holes or blind holes, for example. At least the length L and the width W of each specific element are stored in the database 1. Then physical sections of a number of specific elements are made in step S5, after which photos are made of said sections, which photos are stored in the database 1.
  • the realised layer thickness may also be determined in a non-destructive manner, for example by means of a sonar probe. Using a sonar probe, the realised hole diameter can be measured, from which the layer thickness can be derived.
  • the thickness d 0 of the layer surrounding the hole as well as the thickness d r d n in the layer at several depths in the hole of each specific element are stored in the database.
  • a computer calculation S6 is carried out for calculating a potential distribution U on a macro scale in the electrolyte near the workpiece.
  • the workpiece is divided into grid elements, and the active surface fraction ⁇ of each of said grid elements is determined.
  • the expected local potential difference V-U at the location of the specific element is determined (step S7). Said local potential differences V-U are stored in field V2 of the database 1 and linked to the field V1.
  • the hydrodynamic boundary layer thickness ⁇ influences the rate at which the layer can be deposited on the printed circuit board. Said hydrodynamic boundary layer thickness ⁇ is relevant in particular in the case of blind holes exhibiting a comparatively small length to diameter ratio.
  • step S11 information regarding the printed circuit board, including the layout and the geometric information of the tank (cell) in which the electrolyte is present, is fed to a computer in step S11 , in a manner comparable to step S1. Furthermore, information regarding the global process condition is fed to the computer in step S12, in a manner comparable to the manner in which this information is fed to a computer in step S2.
  • the specific element such as the length to diameter ratio L/W, the type of electrolyte, the process time ⁇ t, etc.
  • the obtained data relating to the specific elements M1 , M2 and M3 are viewed either manually or by means of the computer, and it is determined whether said specific elements yield a value, in particular as regards the expected layer thickness, that ranges between a minimum required layer thickness and a maximum allowable layer thickness at the specific element.
  • the analysis method according to the invention achieves that there is a relatively good chance that a faultless printed circuit board will be directly obtained.
  • a possible solution is to increase the process time ⁇ t and to reduce the total current I proportionally, such that the total amount of electric charge (I x ⁇ t) being delivered remains constant.
  • I x ⁇ t total amount of electric charge
  • an additional counter electrode is disposed near the specific element, so that a greater layer thickness is realised. If the expected layer thickness is too great, a local co-electrode may be disposed opposite the specific element, the effect of said co-electrode being that the expected layer thickness will decrease.
  • Another possible manner of reducing the expected layer thickness is to place an isolation shield near the specific element. Such a shield may be provided with perforations. It is also possible in such a case to add active surface to the workpiece (so-called patches, or an active background grid), as a result of which the active surface fraction ⁇ near the specific element is increased.
  • the potential difference V-U is substantially constant during the process time ⁇ t, which will be the case if a DC power or voltage source is used. It is also possible, however, to set up a similar database and carry out an analysis method if the current is pulsed in time, as is for example the case with pulse plating (PP), which employs a unipolar signal, or in the case of pulse plating reverse (PPR), which employs a bipolar signal, which provides a better layer.
  • PP pulse plating
  • PPR pulse plating reverse
  • Such a bipolar signal is shown in figure 3, in which different currents l c , O, I A and O occur between the workpiece and the counter electrode during different periods t c , t p1 , t A , t p2 .
  • Each period t 0 , t p1 , t A , t p2 is characteristic in the order of a number of milliseconds to a few dozen milliseconds.
  • it is possible to determine the difference V-U at the end of the cathodic pulse for example, for obtaining the local potential difference at the specific element, or to take a time-averaged potential difference V-U for the entire cathodic pulse. It is this current or time-averaged V-U value which is then used for consulting or supplementing the database as described in the foregoing.
  • bipolar signals all the associated values of I and t are stored in the database.
  • Figures 4a-4d show various top plan views of a printed circuit board 2, with figure 4a showing a layout of the conductor pattern 3 arranged on the printed circuit board 2.
  • Figure 4b shows isolines that indicate regions having the same active surface area fraction ⁇ .
  • Figure 4d shows a top plan view of the printed circuit board with isolines of the calculated potential distribution U in the electrolyte near the workpiece.
  • FIG. 5 shows an embodiment of a device 71 suitable for carrying out the method according to the invention.
  • the device 71 is provided with a plate 72 of plastic material disposed in a tank 52, opposite the printed circuit board 53 to be treated, which plate 72 is provided with a grid of passages 73.
  • Elements 31 , 36 are present in a number of passages 73.
  • the other passages 73 are either open or closed by means of plugs (not shown).
  • the elements 31 are connected to an electrically conductive terminal 75 via flexible, insulated wires 74, whilst the elements 36 are connected to an electrically conductive terminal 76 via flexible, insulated wires 74. Opposite potentials may be applied to the terminals 75, 76.
  • the elements 36 are polarised as co-electrodes via the electrically conductive terminal 76, whilst the elements 31 function as counter electrodes via the electrically conductive terminal 75.
  • the elements 36 are polarised as co-electrodes via the electrically conductive terminal 76, whilst the elements 31 function as counter electrodes via the electrically conductive terminal 75.
  • current will flow through the electrolyte between the ends of the elements 36 and the printed circuit board 53 with the pattern 55 provided thereon, and between the ends of the elements 31 and 36.
  • current will flow through electrolyte between the printed circuit board 53 and the counter electrode 54 around the plate 72, and fill the passages 73, which may be open.
  • the positions of the rod-shaped co-electrodes and rod-shaped counter electrodes 36, 31 have been determined by means of the analysis method according to the invention.
  • the printed circuit board 53 treated by means of the device 71 has a layer thickness which corresponds to the desired layer thickness also at the location of the specific elements.
  • the invention has been explained in the figures on the basis of the production of a printed circuit board.
  • the analysis method, the device and the methods are also suitable for treating other surfaces, for example, such as the deposition of a layer of platinum on turbine blades, which blades are provided with cooling channels exhibiting a comparatively large length to diameter ratio L/W. Said cooling channels are to be regarded as being specific elements. It is important that said cooling channels remain open, so that care must be taken upon depositing the layer of platinum on the turbine blades that no layer or substantially no layer is formed in the cooling channels themselves.
  • a specific element may also be an element having a conspicuous dimension, for example exhibiting a comparatively small radius of curvature or a strong change in the radius of curvature or other dimension of an element.

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  • Automation & Control Theory (AREA)
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Abstract

The invention relates, inter alia, to a method for depositing or removing a layer on/from a workpiece, wherein an electrolyte is present between said workpiece and at least one counter electrode and a potential difference is applied between said workpiece and said counter electrode for depositing or removing said layer. The deposition or removal is preceded by an analysis phase, in which an expected layer thickness of the layer to be deposited or removed is calculated on the basis of data from a database. During the analysis phase an expected potential distribution in the electrolyte near the workpiece is calculated, whilst an expected local potential difference between the electrolyte and the workpiece is calculated at least at a specific element on the workpiece. At least the layer thickness at at least one historic specific element stored in the database is retrieved in said database, of which historic specific element at least the local potential difference at least substantially corresponds to the expected local potential difference of the specific element provided on the workpiece, which layer thickness is regarded as the expected layer thickness at the specific element on the workpiece. Subsequently the expected layer thickness is compared to a desired layer thickness at the specific element, whereupon, if the difference between the expected layer thickness and the desired layer thickness exceeds a predetermined value, measures are taken to change the expected local potential difference at the specific element so that the layer thickness to be realised and the desired layer thickness substantially correspond.

Description

A method and a device for depositing or removing a layer on/from a workpiece, an analysis method and device for analysing an expected layer thickness, a method for setting up a database for such an analysis method or device, as well as such a database.
The invention relates to a method for depositing or removing a layer on/from a workpiece, wherein an electrolyte is present between said workpiece and at least one counter electrode and a potential difference is applied between said workpiece and said counter electrode for depositing or removing said layer, which deposition or removal is preceded by an analysis phase, in which an expected layer thickness of the layer to be deposited or removed is calculated on the basis of data from a database.
The invention also relates to a device for depositing or removing a layer on/from a workpiece, which device comprises a tank in which, in use, at least an electrolyte and the workpiece are present, which device further comprises at least one counter electrode and a power or voltage source for applying a potential difference between the workpiece and the counter electrode for depositing or removing the layer on/from the workpiece in use, which deposition or removal process is preceded by an analysis phase, in which an expected layer thickness of the layer to be deposited or removed is calculated on the basis of data from a database.
The invention also relates to an analysis method for analysing an expected layer thickness of the layer to be deposited on or removed from a workpiece, wherein an electrolyte is present between said workpiece and at least one counter electrode and a potential difference is applied between said workpiece and said counter electrode for depositing or removing said layer.
The invention further relates to a device for analysing of an expected layer thickness of the layer to be deposited or one or removed from a workpiece, wherein an electrolyte is present between said workpiece and at least one counter electrode and a potential difference is applied between said workpiece and said counter electrode for depositing or removing said layer.
The invention also relates to a method for setting up a database suitable for use in such an analysis method or device.
The invention further relates to such a database. In such an analysis method, device and method as known from US patent US-B2-6,926,816, a printed circuit board (PCB) surface is divided into a number of grid elements for an arithmetic model wherein an average current density during the deposition or removal of the layer and an active surface area fraction, being the ratio between the electrically conductive area in the grid element that is to be actively treated and the total geometric area of the grid element, is calculated for each specific element. Subsequently, it is determined on the basis of the active surface area fraction α and the calculated current density whether or not the expected layer thickness is acceptable. The grid elements into which the workpiece is divided are relatively large (in the order of mm/cm), so that the total number of regions is limited and the required computer time is also relatively limited.
A drawback of the known method, however, is that in this way an analysis of the layer thickness to be realised at so-called specific elements is not obtained.
A specific element is a relatively small element, usually having a three-dimensional topography, in the workpiece, such as a through hole or a blind hole having a diameter of 0.05-2 mm. The object of the invention is to provide a method for depositing or removing a layer on/from a workpiece which makes it possible to realise a desired layer thickness on the workpiece, and in particular at a specific element. A specific element may for example also be a local elevation or an internal cavity having a small radius of curvature, for example an electrical conductor on an integrated circuit. Such conductors may have a very small width of up to 30 nm. This object is accomplished with the method according to the invention in that
- an expected potential distribution in the electrolyte near the workpiece is calculated during the analysis phase, whilst an expected local potential difference between the electrolyte and the workpiece is calculated at least at a specific element on the workpiece,
- at least the layer thickness at at least one historic specific element stored in the database is retrieved in said database, of which historic specific element at least the local potential difference at least substantially corresponds to the expected local potential difference of the specific element provided on the workpiece, which layer thickness is regarded as the expected layer thickness at the specific element on the workpiece,
- subsequently the expected layer thickness is compared to a desired layer thickness at the specific element, - whereupon, if the difference between the expected layer thickness and the desired layer thickness exceeds a predetermined value, measures are taken to change the expected local potential difference at the specific element so that the layer thickness to be realised and the desired layer thickness substantially correspond. If such a specific element is located in a region having a comparatively low active surface area fraction α, the expected layer thickness at the specific element, i.e. in and around the specific element, will be comparatively large. In that case there is even a risk that the layer deposited at the specific element will fill the specific element entirely, which is undesirable in many applications, such as a through hole or a blind hole in a printed circuit board. Other applications, such as conductors on an integrated circuit, on the other hand require that the specific element be filled entirely, without internal cavity and without any overgrowth over the photoresist layer.
If the active surface area fraction α at the specific element is comparatively high, there is a risk that the layer to be deposited at the specific element will be too thin or even absent altogether around or in the specific element.
By changing the local potential difference between the electrolyte and the workpiece at the specific element on the basis of information regarding similar historic specific elements stored in a database it is achieved that the realised layer thickness substantially corresponds to the desired layer thickness over the entire workpiece, and in particular at the specific element.
The predetermined value of the layer thickness may be a single value, but it may also be a range of values, in which case the expected layer thickness must be within said range. The expected layer thickness must be greater than a minimum desired layer thickness and smaller than a maximum desired layer thickness.
It is noted that from "a new 3D electroplating simulation & design tool", presented at SURFIN 2001 by Roger Mouton, a method for depositing a layer on a workpiece is known wherein an expected layer thickness is calculated on the basis of a theoretical model. The workpiece is then provided with the layer and the actually realised layer thickness on the workpiece is compared with the theoretically expected layer thickness on that specific workpiece.
In contrast to the method according to the invention, Mouton's theoretical model does not make use of a database in which information is stored regarding previously processed workpieces, and in particular regarding realised layer thicknesses at specific elements, at the location of which the local potential difference during the deposition of the layer substantially corresponds to an expected local potential difference at a specific element of the workpiece now to be processed.
The historic specific element with the substantially corresponding local potential difference may be an element of a type and category other than the specific element of the workpiece now to be processed.
An advantage of the use of such a database is amongst others that as more information regarding realised layer thicknesses near specific elements with specific local potential differences and if desired other boundary conditions is stored in the database, the expected layer thickness will corresponds better with the layer thickness actually te be realised near the specific element.
One embodiment of the method according to the invention is characterised in that said measures comprise the placement of at least one co- electrode, an additional counter electrode or an isolation shield near the specific element, so that a local potential difference is obtained, which will result in a desired layer thickness at the specific element.
By placing a counter electrode near the specific element, the local potential difference V-U, wherein U is the local potential in the electrolyte and V is the potential of electrically conductive local part of the workpiece, will become more negative (deposition of material) or more positive (removal of material). This can also be realised by placing an isolation shield near the specific element.
The invention further comprises a device suitable for carrying out the above-described method, which device is characterised in that the device
- is connected to an arithmetic unit for calculating an expected potential distribution in the electrolyte near the workpiece and an expected local potential difference between the electrolyte and the workpiece at at least one specific element on the workpiece, - is connected to a database in which at least layer thicknesses at historic specific elements and as well as the local potential differences during the deposition or removal of the layer are stored,
- is connected to a retrieval unit for retrieving in the database the layer thickness of at least one specific element of which at least the local potential difference at least substantially corresponds to the expected local potential difference near the specific element on the workpiece, which layer thickness is regarded as the expected layer thickness at the specific element on the workpiece,
- is connected to a difference unit for determining the difference between the expected layer thickness and the desired layer thickness at the specific element, as well as for indicating that if the difference exceeds a predetermined value, measures will be taken in the device to change the expected local potential difference at the specific element until the expected layer thickness and the desired layer thickness substantially correspond. Using such a device, it is possible to realise a desired layer thickness over the entire workpiece.
The object of the invention is to provide an analysis method which makes it possible to indicate prior to the deposition or removal of a layer on/from a workpiece whether a desired layer thickness at a specific element can be realised or that additional measures are required.
This object is accomplished with the analysis method according to the invention in that
- an expected potential distribution in the electrolyte near the workpiece is calculated, whilst an expected local potential difference between the electrolyte and the workpiece is calculated at least at a specific element on the workpiece,
- at least the layer thickness at at least one historic specific element stored in a database is retrieved in said database, of which historic specific element at least the local potential difference at least substantially corresponds to the expected local potential difference of the specific element provided on the workpiece, which layer thickness is regarded as the expected layer thickness at the specific element on the workpiece,
- subsequently the expected layer thickness is compared to a desired layer thickness at the specific element, - whereupon, if the difference between the expected layer thickness and the desired layer thickness exceeds a predetermined value, measures are taken to change the expected local potential difference at the specific element so that the expected layer thickness and the desired layer thickness substantially correspond. The potential distribution over the workpiece can be calculated on a macro scale over the workpiece in a simple manner, for which purpose only a limited computer capacity needs to be available, if the workpiece is divided into comparatively large grid elements, each having their own surface area fraction α. The presence of the specific element can be left out of consideration in the determination of the potential distribution U over the workpiece, hardly affects the calculated expected potential distribution U, on account of the very small share of the specific element in the active surface area fraction α in a grid element.
It is also possible to refine the grid elements (higher resolution, for example locally using a grid element dimension of 1 mm instead of 5 mm in other zones of the workpiece) for a region on the workpiece where one or more specific elements that are considered to be critical are located, in order to thus be able to determine the local potential difference V-U near said specific elements with even greater precision. This can be realised without significantly increasing the required computer calculation time. The active surface area fraction α can be calculated as follows:
An (D a - sup
wherein Aact is the area of a grid element that is available for a Faraday reaction, and Asup is the total area of the predetermined grid element.
To determine the electrolyte potential U, use is made of the Laplace equation:
V 2U = O j = - σVU ~2
A precondition on isolating walls and free surfaces (electrolyte level) being that the current density Jn perpendicular to the wall be zero: - - (3)
J - In = Jn = -σWUln = 0
wherein σ is the electrical conductivity of the electrolyte, In i s t h e i n w a rd ve ct o r , perpendicular to the wall. On electrodes said precondition brings the current density Jn and the potential difference between the electrode V and the electrolyte U into connection:
-4
Jn = f(V-U)
For electrodes exhibiting pattern-dependent activity the above precondition can be adapted by means of the local active surface area fraction α:
Jn = α f(V-U) (4bis)
Subsequently the local uniformised current density Jn on a pattern- dependent workpiece (electrode) can be calculated on the basis of the above equation (4bis):
The expected layer thickness d after a predetermined processing time Δt, on the electrode surface, but not at the specific elements, therefore, can then be determined as follows:
. . MMjn -5
Kd - apzF
wherein M is the atomic weight of the metal to be deposited or removed, p is the specific weight of the metal, z is the number of electrons exchanged in the metal reaction, and F is Faraday's constant. By convention, Jn is negative when material is deposited, hence the minus sign in equation (5).
Subsequently the expected local potential difference V-U at the specific element can be obtained in a simple manner on the basis of the calculated potential distribution U over the entire workpiece.
Stored in the database are data of previously produced workpieces and the specific elements thereof, wherein the data relating to a historic specific element stored in the database comprise at least the local potential difference during the treatment of said historic specific element, as well as data regarding the realised layer thickness at said historic specific element. In the database, a historic specific element is retrieved whose local potential difference substantially corresponds to the expected local potential difference of the specific element on the workpiece yet to be treated. The layer thickness of the historic specific element stored in the database is then regarded as the expected layer thickness of the specific element on the workpiece and compared to the desired layer thickness. When relatively large differences are detected, measures will be taken to adjust the expected local potential difference. It has been found that the local potential difference V-LJ is a suitable and relevant value for determining whether the layer thickness to be realised can indeed be realised at the location of a specific element. As appears from equation (4bis), jn/α is also a suitable measure thereof, because a univocal, continuous and monotonous function f brings the two quantities into connection. As appears from the above equations, the expected layer thickness can be accurately determined in a simple manner on the basis of the local potential difference V-U and the active surface area fraction α.
Yet another embodiment of the analysis method according to the invention is characterised in that the specific element comprises a through hole or a blind hole, which hole has a length and a diameter at least substantially the same as the length and the diameter of the specific element to be retrieved in the database.
It has been found that the length and the diameter and/or the length to diameter ratio of a through hole or a blind hole play a major part in the determination whether additional measure are expected to be needed for realising the desired layer thickness.
Thus, only those specific elements that exhibit a comparatively large length to diameter ratio can be analysed by means of the analysis method, for example.
One embodiment of the analysis method according to the invention is characterised in that, in the case of a specific element comprising a through hole, also the pressure difference in the electrolyte on either side of said hole is calculated, wherein substantially the same pressure difference prevailed at the historic specific element to be retrieved in the database upon electrolytic deposition or removal of the layer at said historic specific element.
It has been found that pressure differences in the electrolyte on either side of the through hole have an influence on the layer to be formed or removed near and in the through hole. By adding information regarding the pressure difference that prevailed on either side of a respective historic specific element during the deposition or removal of the layer at said historic specific element to the information regarding historic specific elements stored in the database, a historic specific element can be retrieved in the database which exhibits an even greater resemblance to the specific element on the workpiece, so that even more accurate information regarding the expected layer thickness can be obtained from the database.
Yet another embodiment of the analysis method according to the invention is characterised in that the local hydrodynamic boundary layer thickness in the electrolyte at the specific element is calculated, wherein substantially the same local hydrodynamic boundary layer thickness was found to be present at the historic specific element to be retrieved in the database upon deposition or removal of the layer at said historic specific element.
It has been found that the local hydrodynamic boundary layer thickness affects the layer thickness to be realised. Said hydrodynamic boundary layer thickness can simply be calculated on a macro scale for the entire workpiece and be determined in a simple manner at the location of the specific element on the workpiece. Comparing the specific element on the workpiece to be treated with a historic specific element which exhibited substantially the same local hydrodynamic boundary layer thickness upon deposition or removal of the layer at said historic specific element, makes it possible to realise a more precise determination of the expected layer thickness at the historic specific element on the workpiece.
Yet another embodiment of the analysis method according to the invention is characterised in that the historic specific element to be retrieved in the database was treated in electrolyte substantially the same as the electrolyte in which the workpiece is to be treated. It has been found that the electrolyte is a determining factor as regards the layer thickness to be realised at the specific element.
Yet another embodiment of the analysis method according to the invention is characterised in that if the expected layer thickness is smaller than the desired layer thickness at the specific element, the local potential difference is adjusted by taking measures at least comprising the placement of an additional counter electrode at the specific element.
Said counter electrode preferably has a pin-shaped structure for influencing the potential difference V-U as locally as possible near the specific element whilst influencing the flow of the electrolyte past the workpiece as little as possible.
The counter electrode realises an adjusted local potential difference V-U near the specific element, so that the expected layer thickness will be greater. Yet another embodiment of the analysis method according to the invention is characterised in that if the expected layer thickness is greater than the desired layer thickness at the specific element, the local potential difference is adjusted by taking measures at least comprising the placement of a co-electrode at the specific element, which co-electrode drains part of the current between the counter electrode and the workpiece.
Such a co-electrode reduces the current between the workpiece and the counter electrode at the location of the specific element and also reduces the layer thickness.
The invention further relates to a device, which device comprises - an arithmetic unit for calculating an expected potential distribution in the electrolyte near the workpiece and an expected local potential difference between the electrolyte and the workpiece at at least one specific element on the workpiece,
- a database in which at least layer thicknesses at specific elements and as well as the local potential differences during the deposition or removal of the layer are stored,
- a retrieval unit for retrieving in the database the layer thickness of at least one specific element of which at least the local potential difference at least substantially corresponds to the expected local potential difference at the specific element on the workpiece, which layer thickness is regarded as the expected layer thickness at the specific element on the workpiece,
- a difference unit for determining the difference between the expected layer thickness and the desired layer thickness at the specific element, as well as for indicating that if the difference exceeds a predetermined value, measures must be taken to change the expected local potential difference at the specific element until the expected layer thickness and the desired layer thickness substantially correspond.
As already indicated above, the expected layer thickness can be determined in a simple manner by determining the local potential difference and comparing the specific element with similar specific elements in the database, after which measures may be taken, if desired, to change the local potential difference.
The invention further relates to a method for setting up a database suitable for use with an analysis method and/or device according to the invention. The method according to the invention is characterised in that a layer is deposited on a workpiece or removed from the workpiece, wherein an electrolyte is present between said workpiece and at least one counter electrode and a potential difference is applied between said workpiece and said counter electrode for depositing or removing said layer, after which at least one specific element on the workpiece is selected and subsequently a section of the specific element is made, the data of which section are stored in the database, whilst furthermore the expected potential distribution in the electrolyte near the workpiece as well as an expected local potential difference between the electrolyte and the workpiece at the location of the specific element are calculated, whilst at least the expected local potential difference is stored in the database and linked to the data relating to said section.
By making sections of specific elements, for example by physically dissecting the specific element, information regarding the actually realised layer thickness in and around the specific element is obtained.
It is possible to measure the diameter of a hole at various locations in said hole prior to and after the treatment of the workpiece, with the difference in diameter being the actually realised layer thickness. In this way a section of a specific element is made in a non-destructive manner.
If the workpiece is a printed circuit board provided with dozens, possibly hundreds or even thousands of specific elements, data regarding many specific elements can be collected by producing one or a few printed circuit boards. The database composed by means of the method can be set up by one company and subsequently be made available to various companies that want to use the analysis method and device according to the invention. The invention will now be explained in more detail with reference to the figures, in which:
Figure 1 is a diagram for setting up a database, which database is suitable for use in the analysis method and device according to the invention;
Figure 2 is a diagram showing the analysis method according to the invention;
Figure 3 is a time flow diagram of a bipolar pulsed current signal; Figures 4a-4d are top plan views of a printed circuit board layout, isolines of active surface area fraction α, isolines of a deposited layer thickness distribution and isolines of a potential distribution in the electrolyte along the printed circuit board;
Figure 5 is a perspective view of a device suitable for carrying out the method according to the invention.
The database 1 shown in figure 1 is intended for use in an analysis method for analysing a workpiece, such as a printed circuit board, for example, on which a layer is to be deposited. To deposit the layer, the workpiece and a counter electrode are placed in a tank (cell) containing an electrolyte, and a potential difference is applied between the workpiece and the counter electrode. Said potential difference causes current to flow from the counter electrode through the electrolyte to the workpiece, and an electrochemical reaction will take place at the interface between the electrolyte and the workpiece, as a result of which a metal layer will be deposited on the workpiece. Such a manner of depositing layers is known per se, inter alia from the aforesaid US patent, and will not be explained in more detail herein, therefore.
Preferably, a number of printed circuit boards (PCBs) are produced and tested for setting up a database suitable for use in analysing layer thicknesses on a printed circuit board. In step S1 a printed circuit board is selected and the layout of the circuit to be patterned thereon is stored in a computer. Furthermore, geometric information regarding the tank containing the electrolyte, in which tank the workpiece and the counter electrode are positioned, is stored in a computer. Subsequently, global process conditions are stored in a computer, such as the current I, the time Δt during which the current is applied between the workpiece and the counter electrode, the flow rate of the electrolyte in the tank, the air agitation, the type of electrolyte, the processing temperature, etc. This takes place during S2.
Following that, at least one printed circuit board is produced in step S3.
Of said printed circuit board, a number of specific elements are selected (step S4), which specific elements are through holes or blind holes, for example. At least the length L and the width W of each specific element are stored in the database 1. Then physical sections of a number of specific elements are made in step S5, after which photos are made of said sections, which photos are stored in the database 1. The realised layer thickness may also be determined in a non-destructive manner, for example by means of a sonar probe. Using a sonar probe, the realised hole diameter can be measured, from which the layer thickness can be derived.
Furthermore, the thickness d0 of the layer surrounding the hole as well as the thickness drdn in the layer at several depths in the hole of each specific element are stored in the database.
Furthermore, information of a first type regarding relevant dimensions, such as the length L and the width W, of each specific element, as well as information regarding the electrolyte, such as the supplier, the concentrations used, salts, acids and additives, the process temperature, etc, is stored in the database 1. Also information of a second type regarding position characteristics, such as various values of the layer thicknesses drdn in a hole of the specific element, various values of the layer thickness at special locations in the specific element, the quality of the layer, the layer thickness d0 on the printed circuit board immediately surrounding the hole of the specific element, with the possible addition of digital photos of sections of the specific element, for example in JPG format, is added for each specific element. All this information is stored for each individual specific element in a field V1.
In addition to data regarding the produced printed circuit board, a computer calculation S6 is carried out for calculating a potential distribution U on a macro scale in the electrolyte near the workpiece. For said calculation, the workpiece is divided into grid elements, and the active surface fraction α of each of said grid elements is determined. Then the expected local potential difference V-U at the location of the specific element is determined (step S7). Said local potential differences V-U are stored in field V2 of the database 1 and linked to the field V1.
If desired, a further computer simulation of the flow of the electrolyte may be carried out on a macro scale over the entire printed circuit board (step S8), wherein the pressure difference Ap=P2-P1 and the hydrodynamic boundary layer thickness δ at the specific element can be determined.
Determining a pressure difference in Ap=P2-P1 is in particular important in the case of through holes, in which the length to diameter ratio L/W is relatively small and different pressures P1, p2 occur on either side of the hole. Thus there is a pressure difference Ap=P2-P1 across the hole, which pressure difference results in a flow of electrolyte through the hole. Said flow has an influence on the layer to be formed in the hole.
In the case of blind holes having only one opening and holes having a comparatively large length to diameter ratio L/W, such a pressure difference will hardly lead to a flow of the electrolyte through the holes, if at all, so that the pressure difference Δp can be left out of consideration with holes of this type.
The hydrodynamic boundary layer thickness δ influences the rate at which the layer can be deposited on the printed circuit board. Said hydrodynamic boundary layer thickness δ is relevant in particular in the case of blind holes exhibiting a comparatively small length to diameter ratio. The local pressure difference Ap=P2-P1 and the hydrodynamic boundary layer thickness δ are determined in step S9 and stored in field V3 of the database, which field V3 is linked to the associated fields V1 and V2 of a specific element. Each time a printed circuit board has been produced and sections of specific elements have been made, whether or not in a destructive manner, it is possible to store the information obtained therefrom in the database 1 together with the information from the computer simulation, so that an increasing number of specific elements and associated data are to be found in the database 1. Figure 2 shows a diagram of the analysis method according to the invention, which analysis method can be carried out by means of a device according to the invention.
If a layer is to be deposited on a new printed circuit board provided with a number of blind holes and a number of through holes, information regarding the printed circuit board, including the layout and the geometric information of the tank (cell) in which the electrolyte is present, is fed to a computer in step S11 , in a manner comparable to step S1. Furthermore, information regarding the global process condition is fed to the computer in step S12, in a manner comparable to the manner in which this information is fed to a computer in step S2.
Prior to the actual production of the desired printed circuit boards, computer simulations are carried out in a manner comparable to steps S6, S7, S8 and S9, and specific elements are selected (step S14), wherein the local potential difference V-U at the location of the specific elements is calculated, as well as the pressure difference Ap=P2-P1, if desired, and the hydrodynamic boundary layer thickness δ. Preferably, as much information as possible is collected of each specific element, such as the length to diameter ratio L/W, the type of electrolyte, the process time Δt, etc. Following that, information relating to those specific elements M1 , M2 and M3 of which the data and at least the expected local potential difference V-U correspond as much as possible, and preferably entirely, with the specific element to be analysed is retrieved from the database 1 in step S20.
Then the obtained data relating to the specific elements M1 , M2 and M3 are viewed either manually or by means of the computer, and it is determined whether said specific elements yield a value, in particular as regards the expected layer thickness, that ranges between a minimum required layer thickness and a maximum allowable layer thickness at the specific element.
If such is the case, and this also holds for all the other specific elements on the printed circuit board, the actual production of the printed circuit board can be started. The analysis method according to the invention achieves that there is a relatively good chance that a faultless printed circuit board will be directly obtained.
Additional measures need to be taken if the layer thickness of the retrieved specific elements M1 , M2 and M3 is smaller or greater than a specific desired layer thickness or smaller than a minimum required layer thickness or greater than a maximum allowable layer thickness around or in the specific element on the workpiece.
A possible solution is to increase the process time Δt and to reduce the total current I proportionally, such that the total amount of electric charge (I x Δt) being delivered remains constant. A lower total current leads to a more uniform layer thickness distribution over the printed circuit board and in the specific elements, although this will lead to a longer process time and thus a loss of production capacity.
Preferably, an additional counter electrode is disposed near the specific element, so that a greater layer thickness is realised. If the expected layer thickness is too great, a local co-electrode may be disposed opposite the specific element, the effect of said co-electrode being that the expected layer thickness will decrease. Another possible manner of reducing the expected layer thickness is to place an isolation shield near the specific element. Such a shield may be provided with perforations. It is also possible in such a case to add active surface to the workpiece (so-called patches, or an active background grid), as a result of which the active surface fraction α near the specific element is increased.
With regard to the database 1 shown in figure 1 and figure 2 it has been assumed that the potential difference V-U is substantially constant during the process time Δt, which will be the case if a DC power or voltage source is used. It is also possible, however, to set up a similar database and carry out an analysis method if the current is pulsed in time, as is for example the case with pulse plating (PP), which employs a unipolar signal, or in the case of pulse plating reverse (PPR), which employs a bipolar signal, which provides a better layer. Such a bipolar signal is shown in figure 3, in which different currents lc, O, IA and O occur between the workpiece and the counter electrode during different periods tc, tp1, tA, tp2. Each period t0, tp1, tA, tp2 is characteristic in the order of a number of milliseconds to a few dozen milliseconds. In such a case it is possible to determine the difference V-U at the end of the cathodic pulse for example, for obtaining the local potential difference at the specific element, or to take a time-averaged potential difference V-U for the entire cathodic pulse. It is this current or time-averaged V-U value which is then used for consulting or supplementing the database as described in the foregoing. When bipolar signals are used, all the associated values of I and t are stored in the database.
Figures 4a-4d show various top plan views of a printed circuit board 2, with figure 4a showing a layout of the conductor pattern 3 arranged on the printed circuit board 2.
Figure 4b shows isolines that indicate regions having the same active surface area fraction α. As already indicated in the foregoing, if no additional measures are taken, there is a relatively good chance that the expected layer thickness at specific elements 4 in regions having a comparatively high active surface area fraction α will be too small, whilst there is a good chance that the layer thickness at specific elements 5 in a region having a comparatively low active surface area fraction α will be too large. It is advisable to use the analysis method according to the invention for specific elements 4, 5 in such regions. Also other specific elements, for example elements exhibiting a relatively large length to diameter ratio L/W, merit special attention in order to be able to ensure that the layer thickness will be sufficient over the entire length L of such a specific element.
Using the computer, an expected layer thickness distribution over the printed circuit board 2, expressed in μm, has been calculated partially on the basis of the information obtained from figure 4b, which distribution is shown in figure 4c.
Figure 4d shows a top plan view of the printed circuit board with isolines of the calculated potential distribution U in the electrolyte near the workpiece. The situation shown in figure 4d has been calculated for a workpiece potential V = O Volt, so that the numbers shown in figure 4d represent the value V-U without a minus sign.
As already indicated above, a comparatively limited computer capacity sufficies for calculating the potential distribution U over the entire area of the workpiece. The specific elements may be left out of consideration in this regard, since they hardly affect the potential distribution U.
Figure 5 shows an embodiment of a device 71 suitable for carrying out the method according to the invention. The device 71 is provided with a plate 72 of plastic material disposed in a tank 52, opposite the printed circuit board 53 to be treated, which plate 72 is provided with a grid of passages 73. Elements 31 , 36 are present in a number of passages 73. The other passages 73 are either open or closed by means of plugs (not shown). The elements 31 are connected to an electrically conductive terminal 75 via flexible, insulated wires 74, whilst the elements 36 are connected to an electrically conductive terminal 76 via flexible, insulated wires 74. Opposite potentials may be applied to the terminals 75, 76. The elements 36 are polarised as co-electrodes via the electrically conductive terminal 76, whilst the elements 31 function as counter electrodes via the electrically conductive terminal 75. During the operation of the device 71 , current will flow through the electrolyte between the ends of the elements 36 and the printed circuit board 53 with the pattern 55 provided thereon, and between the ends of the elements 31 and 36. Moreover, current will flow through electrolyte between the printed circuit board 53 and the counter electrode 54 around the plate 72, and fill the passages 73, which may be open. The positions of the rod-shaped co-electrodes and rod-shaped counter electrodes 36, 31 have been determined by means of the analysis method according to the invention. The printed circuit board 53 treated by means of the device 71 has a layer thickness which corresponds to the desired layer thickness also at the location of the specific elements. The invention has been explained in the figures on the basis of the production of a printed circuit board. The analysis method, the device and the methods are also suitable for treating other surfaces, for example, such as the deposition of a layer of platinum on turbine blades, which blades are provided with cooling channels exhibiting a comparatively large length to diameter ratio L/W. Said cooling channels are to be regarded as being specific elements. It is important that said cooling channels remain open, so that care must be taken upon depositing the layer of platinum on the turbine blades that no layer or substantially no layer is formed in the cooling channels themselves.
Instead of depositing a layer on a workpiece, it is also possible to remove a layer from defined areas of a workpiece, or to ensure that no layer will be formed or no layer will be removed at a specific element, for example.
A specific element may also be an element having a conspicuous dimension, for example exhibiting a comparatively small radius of curvature or a strong change in the radius of curvature or other dimension of an element.

Claims

1. A method for depositing or removing a layer on/from a workpiece, wherein an electrolyte is present between said workpiece and at least one counter electrode and a potential difference is applied between said workpiece and said counter electrode for depositing or removing said layer, which deposition or removal is preceded by an analysis phase, in which an expected layer thickness of the layer to be deposited or removed is calculated on the basis of data from a database, characterised in that - an expected potential distribution in the electrolyte near the workpiece is calculated during the analysis phase, whilst an expected local potential difference between the electrolyte and the workpiece is calculated at least at a specific element on the workpiece,
- at least the layer thickness at at least one historic specific element stored in the database is retrieved in said database, of which historic specific element at least the local potential difference at least substantially corresponds to the expected local potential difference of the specific element provided on the workpiece, which layer thickness is regarded as the expected layer thickness at the specific element on the workpiece, - subsequently the expected layer thickness is compared to a desired layer thickness at the specific element,
- whereupon, if the difference between the expected layer thickness and the desired layer thickness exceeds a predetermined value, measures are taken to change the expected local potential difference at the specific element so that the layer thickness to be realised and the desired layer thickness substantially correspond.
2. A method according to claim 1 , characterised in that said measures comprise the placement of at least one co-electrode, an additional counter electrode or an isolation shield near the specific element, so that a local potential difference is obtained, which will result in a desired layer thickness at the specific element.
3. A device for depositing or removing a layer on/from a workpiece, which device comprises a tank in which, in use, at least an electrolyte and the workpiece are present, which device further comprises at least one counter electrode and a power or voltage source for applying a pull potential difference between the workpiece and the counter electrode for depositing or removing the layer on/from the workpiece in use, which deposition or removal process is preceded by an analysis phase, in which an expected layer thickness of the layer to be deposited or removed is calculated on the basis of data from a database, characterised in that the device - is connected to an arithmetic unit for calculating an expected potential distribution in the electrolyte near the workpiece and an expected local potential difference between the electrolyte and the workpiece at at least one specific element on the workpiece,
- is connected to a database in which at least layer thicknesses at historic specific elements and as well as the local potential differences during the deposition or removal of the layer are stored,
- is connected to a retrieval unit for retrieving in the database the layer thickness of at least one specific element of which at least the local potential difference at least substantially corresponds to the expected local potential difference near the specific element on the workpiece, which layer thickness is regarded as the expected layer thickness at the specific element on the workpiece,
- is connected to a difference unit for determining the difference between the expected layer thickness and the desired layer thickness at the specific element, as well as for indicating that if the difference exceeds a predetermined value, measures will be taken in the device to change the expected local potential difference at the specific element until the expected layer thickness and the desired layer thickness substantially correspond.
4. A device according to claim 3, characterised in that the measures taken in the device comprise the provision of at least one co-electrode, an additional counter electrode or an isolation shield near the specific element for the purpose of obtaining a local potential difference which will result in a desired layer thickness at the specific element.
5. An analysis method for analysing an expected layer thickness of the layer to be deposited on or removed from a workpiece, wherein an electrolyte is present between said workpiece and at least one counter electrode in use and a potential difference is applied between said workpiece and said counter electrode for depositing or removing the layer, characterised in that
- an expected potential distribution in the electrolyte near the workpiece is calculated, whilst an expected local potential difference between the electrolyte and the workpiece is calculated at least at a specific element on the workpiece,
- at least the layer thickness at at least one historic specific element stored in a database is retrieved in said database, of which historic specific element at least the local potential difference at least substantially corresponds to the expected local potential difference of the specific element provided on the workpiece, which layer thickness is regarded as the expected layer thickness at the specific element on the workpiece,
- subsequently the expected layer thickness is compared to a desired layer thickness at the specific element,
- whereupon, if the difference between the expected layer thickness and the desired layer thickness exceeds a predetermined value, measures are taken to change the expected local potential difference at the specific element so that the expected layer thickness and the desired layer thickness substantially correspond.
6. An analysis method according to claim 5, characterised in that the specific element is an element on the workpiece whose dimensions are smaller than the dimensions of a grid element of an arithmetic model used for calculating the local potential difference at the specific element.
7. An analysis method according to claim 5 or 6, characterised in that the specific element is an element on the workpiece of which at least one dimension is either smaller or larger than a predetermined value.
8. An analysis method according to any one of the preceding claims 5-7, characterised in that the specific element comprises a through hole or a blind hole, which hole has a length and a diameter at least substantially the same as the length and the diameter of the specific element to be retrieved in the database.
9. An analysis method according to claim 8, characterised in that the workpiece is provided with a number of specific elements, the length to diameter ratio of all of which specific elements is determined, after which the local potential difference of at least the specific elements exhibiting the largest length to diameter ratios is calculated and changed, if desired.
10. An analysis method according to any one of the preceding claims 5-9, characterised in that, in the case of a specific element comprising a through hole, also the pressure difference in the electrolyte on either side of said hole is calculated, wherein substantially the same pressure difference prevailed at the historic specific element to be retrieved in the database upon electrolytic deposition or removal of the layer at said historic specific element.
11. An analysis method according to any one of the preceding claims 5-10, characterised in that the local hydrodynamic boundary layer thickness in the electrolyte at the specific element is calculated, wherein substantially the same local hydrodynamic boundary layer thickness was found to be present at the historic specific element to be retrieved in the database upon deposition or removal of the layer at said historic specific element.
12. An analysis method according to any one of the preceding claims 5-11 , characterised in that the historic specific element to be retrieved in the database was treated in electrolyte substantially the same as the electrolyte in which the workpiece is to be treated.
13. An analysis method according to any one of the preceding claims 5-12, characterised in that if the expected layer thickness is smaller than the desired layer thickness at the specific element, the local potential difference is adjusted by taking measures at least comprising the placement of an additional counter electrode at the specific element.
14. An analysis method according to any one of the preceding claims 5-13, characterised in that if the expected layer thickness is greater than the desired layer thickness at the specific element, the local potential difference is adjusted by taking measures at least comprising the placement of a co-electrode at the specific element, which co-electrode drains part of the current between the counter electrode and the workpiece.
15. An analysis method according to any one of the preceding claims 5-14, characterised in that if the expected layer thickness is greater than the desired layer thickness at the specific element, the local potential difference is adjusted by taking measures at least comprising the placement of conductive material on the workpiece near the specific element.
16. A device for analysing of an expected layer thickness of the layer to be deposited on or removed from a workpiece, wherein an electrolyte is present between said workpiece and at least one counter electrode in use and a potential difference is applied between said workpiece and said counter electrode for depositing or removing said layer, characterised in that the device comprises
- an arithmetic unit for calculating an expected potential distribution in the electrolyte near the workpiece and an expected local potential difference between the electrolyte and the workpiece at at least one specific element on the workpiece,
- a database in which at least layer thicknesses at specific elements and as well as the local potential differences during the deposition or removal of the layer are stored,
- a retrieval unit for retrieving in the database the layer thickness of at least one specific element of which at least the local potential difference at least substantially corresponds to the expected local potential difference at the specific element on the workpiece, which layer thickness is regarded as the expected layer thickness at the specific element on the workpiece,
- a difference unit for determining the difference between the expected layer thickness and the desired layer thickness at the specific element, as well as for indicating that if the difference exceeds a predetermined value, measures must be taken to change the expected local potential difference at the specific element until the expected layer thickness and the desired layer thickness substantially correspond.
17. A method for setting up a database suitable for use in an analysis method according to any one of the preceding claims 5-15, characterised in that a layer is deposited on a workpiece or removed from the workpiece, wherein an electrolyte is present between said workpiece and at least one counter electrode and a potential difference is applied between said workpiece and said counter electrode for depositing or removing said layer, after which at least one specific element on the workpiece is selected and subsequently a section of the specific element is made, the data of which section are stored in the database, whilst furthermore the expected potential distribution in the electrolyte near the workpiece as well as an expected local potential difference between the electrolyte and the workpiece at the location of the specific element are calculated, whilst at least the expected local potential difference is stored in the database and linked to the data relating to said section.
18. A method according to claim 17, characterised in that the specific element comprises a through hole, wherein the pressure difference in the electrolyte on either side of the hole is calculated, stored in the database and linked to the data relating to said section.
19. A method according to claim 17 or 18, characterised in that the local hydrodynamic boundary layer thickness δ in the electrolyte at the specific element is calculated, stored in the database and linked to the data relating to said section.
20. A method according to any one of the preceding claims 17-19, characterised in that furthermore data regarding the electrolyte used, the dimensions of the specific element and/or the duration of the treatment are stored in the database for each specific element and linked to the data relating to said section.
21. A database set up by using the method according to any one of the preceding claims 17-20.
Figure 1
51 Select a workpiece or PCB layout and plating cell configuration
52 Define the global process conditions I, Δt, liquid delivery, air agitation, bad type, temperature
54 Select a specific element
53 Carry out an industrial test
S6 Carry out a macro scale potential model computer simulation
58 Carry out a macro scale liquid flow computer simulation
55 Make a destructive section of the specific element
56 Measure the potential V-U value at the correct location of the specific element
59 Measure the δ or (p2 and p1 ) value at the correct location of the specific element
photo
V3 δ or (p2 and p1)
Database cell Figure 2
511 Select a workpiece or PCB layout and plating cell configuration
512 Define the global process conditions I, Δt, liquid delivery, air agitation, bad type, temperature
S14 Select a specific element
516 Carry out a macro scale potential model computer simulation
518 Carry out a macro scale liquid flow computer simulation
517 Measure the potential V-U value at the correct location of the specific element
519 Measure the δ or (p2 and p1 ) value at the correct location of the specific element
δ or (p2 and p1 )
520 Explore database
Selected database cells
PCT/IB2008/001905 2007-06-12 2008-06-09 A method and a device for depositing or removing a layer on/from a workpiece, an analysis method and device for analysing an expected layer thickness, a method for setting up a database for such an analysis method or device, as well as such a database WO2008152506A2 (en)

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NL1033973A NL1033973C2 (en) 2007-06-12 2007-06-12 Method and device for depositing or removing a layer on a workpiece, analysis method and device for analyzing an expected layer thickness, a method for manufacturing a database for such an analysis method or device, and such a database.
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NL2007221C2 (en) * 2011-08-04 2013-02-05 Elsyca N V A device suitable for the electrochemical processing of an object, a holder suitable for such a device and a method for the electrochemical processing of an object.
EP2754735A1 (en) 2013-01-11 2014-07-16 Elsyca N.V. A device suitable for the electrochemical processing of an object, a holder suitable for such a device and a method for the electrochemical processing of an object
US9677191B2 (en) 2013-01-17 2017-06-13 Elsyca N.V. Device suitable for the electrochemical processing of an object, a holder suitable for such a device, and a method for the electrochemical processing of an object

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NL2007221C2 (en) * 2011-08-04 2013-02-05 Elsyca N V A device suitable for the electrochemical processing of an object, a holder suitable for such a device and a method for the electrochemical processing of an object.
EP2754735A1 (en) 2013-01-11 2014-07-16 Elsyca N.V. A device suitable for the electrochemical processing of an object, a holder suitable for such a device and a method for the electrochemical processing of an object
US9677191B2 (en) 2013-01-17 2017-06-13 Elsyca N.V. Device suitable for the electrochemical processing of an object, a holder suitable for such a device, and a method for the electrochemical processing of an object

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