GB2448313A - Method and apparatus for determining screen printer stroke direction - Google Patents

Method and apparatus for determining screen printer stroke direction Download PDF

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Publication number
GB2448313A
GB2448313A GB0706822A GB0706822A GB2448313A GB 2448313 A GB2448313 A GB 2448313A GB 0706822 A GB0706822 A GB 0706822A GB 0706822 A GB0706822 A GB 0706822A GB 2448313 A GB2448313 A GB 2448313A
Authority
GB
United Kingdom
Prior art keywords
solder paste
deposit
screen printer
deposits
slope
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
GB0706822A
Other versions
GB0706822D0 (en
Inventor
James Mahon
Peter Conlon
James Tracey
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
MV Res Ltd
Original Assignee
MV Res Ltd
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 MV Res Ltd filed Critical MV Res Ltd
Priority to GB0706822A priority Critical patent/GB2448313A/en
Publication of GB0706822D0 publication Critical patent/GB0706822D0/en
Publication of GB2448313A publication Critical patent/GB2448313A/en
Withdrawn legal-status Critical Current

Links

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
    • H05K3/10—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern
    • H05K3/12—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using thick film techniques, e.g. printing techniques to apply the conductive material or similar techniques for applying conductive paste or ink patterns
    • H05K3/1216—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using thick film techniques, e.g. printing techniques to apply the conductive material or similar techniques for applying conductive paste or ink patterns by screen printing or stencil printing
    • H05K3/1233—Methods or means for supplying the conductive material and for forcing it through the screen or stencil
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41F—PRINTING MACHINES OR PRESSES
    • B41F15/00—Screen printers
    • B41F15/14—Details
    • 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
    • H05K3/10—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern
    • H05K3/12—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using thick film techniques, e.g. printing techniques to apply the conductive material or similar techniques for applying conductive paste or ink patterns
    • H05K3/1216—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using thick film techniques, e.g. printing techniques to apply the conductive material or similar techniques for applying conductive paste or ink patterns by screen printing or stencil printing
    • 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
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/0266—Marks, test patterns or identification means
    • H05K1/0269—Marks, test patterns or identification means for visual or optical inspection
    • 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
    • H05K2203/0139—Blade or squeegee, e.g. for screen printing or filling of holes
    • 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
    • H05K2203/16—Inspection; Monitoring; Aligning
    • H05K2203/163—Monitoring a manufacturing process

Abstract

The present invention relates to a method and apparatus for determining the stroke direction of a screen printer by measuring the height of solder paste deposits on the PCB and using these to calculate the slope. The slope can than be associated with a specific stroke direction of the screen printer. The stoke direction can then by associated with various measurement data taken from a PCB and used to facilitate control of the screen printer.

Description

Method and Apparatus for Determining Screen Printer Sfroke Direction
The present invention relates to a method and apparatus for detemiining the stoke direction of a screen printer.
Currently solder paste is screen printed on to printed circuit boards (PCB) as the first stage in the surface mount technology (SMT) manufacturing process. During the printing process solder paste is pressed through a stencil by a squeegee on to the PCB. in order to achieve consistently high paste print quality the printer presents the user with many control variables, such as stencil XY offset, stencil orientation, squeegee level, squeegee pressure, squeegee speed and so on.
Typically modem paste printers have two squeegees, one that will print in the forward direction and one that will print in the reverse direction. This is also referred to as the screen printer stroke direction. For control purposes this essentially means that there are two separate paste printers in one machine.
After printing the SMT production line may include a solder paste inspection (SPI) machine. This machine inspects each paste deposit printed for XY offset, height, area and volume. This measurement data can be used to control the paste print process. However if the print parameters are to be controlled properly it is critically important that the controller knows which squeegee was used to print the solder paste on the PCB. Or in other words, the controller must know the stroke direction of the screen printer.
I
It is an object of the present invention to address the above mentioned technical problem of detecting the stroke direction of the screen printer.
According to the present invention, that object is achieved by means of a method and apparatus having the features set forth in the claims that follow, such claims being an integral part of the present disclosure.
Advantageously, the present invention ensures that paste measurements are separated according to squeegee, or stroke direction therefore ensuring that the correct print control parameters are sent back to the paste printer.
While the principle advantages and features of the invention have been described above, a greater understanding and appreciation of the invention may be obtained by referring to the drawings and detailed description of the various embodiments, presented by way of example only, in which: Figure 1 shows a block diagram of a first embodiment of the present invention, Figures 2a depicts the slope of a paste deposit printed in the forward stoke direction, Figures 2b depicts the slope of a paste deposit printed in the reverse stoke direction, Figure 3 shows a variety of solder paste deposits on a PCB, Figure 4 shows a block diagram of a second embodiment of the present invention, FigureS shows a block diagram of a third embodiment of the present invention, Figure 6 depicts solder paste offset, Figure 7 is a graph of solder paste offset measurement, and Figure 8 shows yet a forth embodiment of the present invention.
According to the first embodiment of the present invention, in order to correctly control a printer, the printer manufacture would have to react to SPI measurement data. This would only be possible if board serialisation was implemented (i.e. use of unique barcodes). As shown in figure 1, the screen printer would keep a record of the squeegee direction for a given barcode and would match with SPI measurement data to make printer adjustments.
According to the second embodiment of the present invention, the method described below can be used to implement closed loop (automatic or manual) control on any paste printer. The method does not require any input from the paste printer other than for an operator to indicate the starting stroke direction in a board print sequence. The SPI machine can be placed at any position in the SMT line, for example, before the reflow as there is no need to perform Solder Paste inspection immediately after paste screening.
An important element of this invention is the separation of SPI measurement data into two streams; one for forward printing and one for reverse printing. This can be achieved using 3D data, such as then height of a paste deposit. The height can be determined using such known techniques as optical inspection, in particular, laser triangulation.
Figures 2a and 2b depicting a paste deposit whose long axis is parallel to the direction of travel of the printer squeegee. It is a general characteristic of the printing process that deposits will slope upwards in the direction of squeegee movement.
A SPI system creates 3D range maps of deposits from which the slope of the deposit can be determined. The slope is determined by measuring the height of the paste deposit at two different points on the deposit. These points are preferably at opposite ends of a rectangular shaped deposit.
The system can then observe that on average for a number of deposits on the PCB that the slope of the deposit is generally in one direction and from this slope direction the squeegee direction can be inferred.
Alternatively, more than two points on a paste deposit can be measured for height and used to determine the slope.
Figure 3 shows that not all deposits printed on a PCB are suitable when trying to determine global stroke direction. Suitable application software can choose paste deposits which are longest in the direction of printing, rectangular deposits parallel to the print direction for instance.
Figure 4 shows an SMT line layout as disclosed in the second embodiment of the present invention, in which the slope is calculated and used to determine the stroke direction of the screen printer. This information is feed back to the screen printer to facilitate control of the screen printer.
As show in figure 5, a third embodiment of the present invention determines stoke direction of the screen printer from the analysis of 2D paste deposit data.
This 2D analysis can make use of such know techniques as Photometric Stereo and Global Deposit Offset.
Photometric stereo techniques, while originally intended to enhance placed component inspection, has sufficient resolution to allow the determination of global paste deposit slope from 2D image data, and thus the screen printer stoke direction.
Alternatively, the offset data can be analysed as shown in figure 6 and a characteristic "zig-zag" pattern can be observed, as shown in figure 7.
Using a 2D inspection machine in conjunction with a data analysis tool it is possible to generate two separate offset data streams, one for either print direction. In this case the user would have to determine the starting print direction so that data streams can be assigned to an individual print direction.
In the case where long periods between inspections is observed the sequence of squeegee print direction may have changed, due perhaps to a clean cycle. For this situation the user may have to re-establish the starting print direction.
In yet a forth embodiment of the present invention, as shown in figure 8, a screen print manufacturer can indicate the screen print direction by making a readable mark on all boards of one print direction. In this way, it would be vezy simple for any inspection company to aggregate data by stroke direction. This technique would not require barcodes or electronic communication between machines.
Once screen print direction has been derived using any of the embodiments discussed above the measurement data can be feedback to the paste printer either automatically or manually.
When feeding back print offset data (for the whole board), offsets must be made with reference to the centre of rotation of the stencil in the paste printer which will not be the same as the centre of mass of the deposits as inspected by the SPI machine.
Feedback of print performance could take place after every inspection letting the printer determine exactly how to use the measurement lata Feedback could also take place by using process control algorithms/techniques where adjustments would be made when necessary, thereby removing the effects of measurement noise'.
It is not intended that the present invention be limited to the above embodiments and other modifications and variations are envisaged within the scope of the claims.

Claims (12)

  1. Claims 1. A method of determining screen printer stroke direction, the
    method comprising the steps of: measuring height of a solder paste deposit located on a PCB at a first point on the solder paste deposit, measuring height of the solder paste deposit at a second point on the solder paste deposit, calculating a slope of the solder paste deposit based on the measured height at the first and second points of the solder paste deposit, associating the slope of the solder paste deposit with a stoke direction used by the screen printer during deposition of the solder paste deposit.
  2. 2. A method as claimed in claim!, wherein the method further comprises the steps of: measuring height a plurality of solder paste deposits at first and seconds points on each solder paste deposit, calculating a slope for each of the plurality of solder paste deposits, averaging the slopes of each solder paste deposit to calculate an overall slope of the paste deposits on the PCB, associating the overall slope of the paste deposits on the PCB with a stoke direction used by the screen printer during deposition of the solder paste deposit.
  3. 3. A method as claimed in any preceding claim, wherein the measured solder paste deposits are rectangular shaped.
  4. 4. A method as claimed in any preceding claim, wherein the measured solder paste deposits are parallel to the stroke direction of the screen printer.
  5. 5. A method of controlling a screen printer, the method comprising the steps of: detenninrng stroke direction of the screen printer by analysis of a solder paste deposited on a PCB, and associating the stoke direction with measurement data in order to facilitate control of the screen printer.
  6. 6. Apparatus for determining screen printer stroke direction, comprising: means for measuring height of a solder paste deposit located on a PCB at a first point on the solder paste deposit, means for measuring height of the solder paste deposit at a second point on the solder paste deposit, means for calculating a slope of the solder paste deposit based on the measured height at the first and second points of the solder paste deposit, means for associating the slope of the solder paste deposit with a stoke direction used by the screen printer during deposition of the solder paste deposit.
  7. 7. Apparatus as claimed in claim 6, wherein the apparatus further comprises: means for measuring height a plurality of solder paste deposits at first and seconds points on each solder paste deposit, means for calculating a slope for each of the plurality of solder paste deposits, means for averaging the slopes of each solder paste deposit to calculate an overall slope of the paste deposits on the P03, means for associating the overall slope of the paste deposits on the PCB with a stoke direction used by the screen printer during deposition of the solder paste deposit.
  8. 8. Apparatus as claimed in claims 6-7, wherein the measured solder paste deposits are rectangular shaped.
  9. 9. Apparatus as claimed in claim 6-8, wherein the measured solder paste deposits are parallel to the stroke direction of the screen printer.
  10. 10. Apparatus as claimed in claim 6-9, wherein optical techniques are used for measuring the height of the solder paste deposits.
  11. 11. Apparatus as claimed in claim 10, wherein the optical technique is laser triangulation.
  12. 12. A method and/or apparatus as hereinbefore described and with references to the accompanying figures.
GB0706822A 2007-04-10 2007-04-10 Method and apparatus for determining screen printer stroke direction Withdrawn GB2448313A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB0706822A GB2448313A (en) 2007-04-10 2007-04-10 Method and apparatus for determining screen printer stroke direction

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB0706822A GB2448313A (en) 2007-04-10 2007-04-10 Method and apparatus for determining screen printer stroke direction

Publications (2)

Publication Number Publication Date
GB0706822D0 GB0706822D0 (en) 2007-05-16
GB2448313A true GB2448313A (en) 2008-10-15

Family

ID=38091038

Family Applications (1)

Application Number Title Priority Date Filing Date
GB0706822A Withdrawn GB2448313A (en) 2007-04-10 2007-04-10 Method and apparatus for determining screen printer stroke direction

Country Status (1)

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GB (1) GB2448313A (en)

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0935135A1 (en) * 1998-02-09 1999-08-11 MV Research Limited System for measuring solder bumps
GB2350320A (en) * 1999-03-25 2000-11-29 Matsushita Electric Ind Co Ltd Squeegee for screen printing that agitates, rotates and fills
GB2351259A (en) * 1999-06-22 2000-12-27 Dek Printing Machines Ltd Blades for screen printing
GB2362132A (en) * 2000-05-09 2001-11-14 Matsushita Electric Ind Co Ltd Screen printing apparatus for a printed circuit board having defect measuring and inspection means
GB2367034A (en) * 2000-07-18 2002-03-27 Matsushita Electric Ind Co Ltd Screen printing apparatus
GB2377410A (en) * 2001-07-12 2003-01-15 Matsushita Electric Ind Co Ltd Squeegee head with means for both filling and wiping a mask plate

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0935135A1 (en) * 1998-02-09 1999-08-11 MV Research Limited System for measuring solder bumps
GB2350320A (en) * 1999-03-25 2000-11-29 Matsushita Electric Ind Co Ltd Squeegee for screen printing that agitates, rotates and fills
GB2351259A (en) * 1999-06-22 2000-12-27 Dek Printing Machines Ltd Blades for screen printing
GB2362132A (en) * 2000-05-09 2001-11-14 Matsushita Electric Ind Co Ltd Screen printing apparatus for a printed circuit board having defect measuring and inspection means
GB2367034A (en) * 2000-07-18 2002-03-27 Matsushita Electric Ind Co Ltd Screen printing apparatus
GB2377410A (en) * 2001-07-12 2003-01-15 Matsushita Electric Ind Co Ltd Squeegee head with means for both filling and wiping a mask plate

Also Published As

Publication number Publication date
GB0706822D0 (en) 2007-05-16

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WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)