DE10355990A1 - Differential etching technique for plate shaped components e.g. electronic circuit board, comprises using an etching unit with a horizontal or vertical transport system - Google Patents

Abstract

A process for differentially etching plate shaped components with laminated metal films on one or both sides, comprises using an etching unit with a horizontal or vertical transport system. The etch rate is reduced over the edge region, so it remains thicker than the rest of the plate. An injector is used to feed gas into the etching fluid.

Description

The The invention relates to the chemical etching of the surface of large area, flat good, at least on one side with a metal foil is laminated. The metal foil is supposed to be reduced in thickness by the etching become. This process will as difference sentences or thinning. Preferred field of application is the etching of laminated base material for the Printed circuit board technology by means of an etching liquid.

to Production of printed circuit boards and conductor foils in fine conductor technology the thickness of the laminated on an electrically non-conductive core Copper foil not more than 5 μm be. Thicker laminated films can be used as the base layer later Completing the circuit diagram of the circuit boards, especially during the etching of these Base layer to inaccurate structures and unacceptable etching errors to lead. Base materials with such thin Copper laminations are commercially available available. Because of the effort involved in making these thin felts is to be provided, however, incur high production costs. Based materials with 17 μm or 35 μm Copper laminates are available at considerably lower cost. That's why they are preferred used these base materials. By differential etching the Kupferkaschierung thinned back to the required thickness.

At the Conductor image structure, the conductor pattern is one-sided or negative on both sides on the Kupferkaschierung the base material by means of an electrically not conductive galvanoresist applied. The conductor tracks and the holes are then electrolytically z. B. reinforced by 25 microns and then with an etch resist Mistake. This can be z. B. a 4 microns thick tin layer as a metal resist.

To Removal of the Galvanoresistes is used to produce the structures chemically etched the copper lining, which is not metal resistant is protected. When the thickness of this lamination on the order of reinforcing applied conductor runs is, then a correspondingly long etching time is required to to get to the insulating base layer. In the fine conductor technology with intervals of conductor runs in the order of magnitude the thickness of these conductors, it can cause etching defects as well as with long etching times too unwanted underetchings come. These problems increase as the thickness of the laminations increases of the base material too. Therefore one uses with the Feinleitertechnik Lamination thicknesses of 4 to 5 μm copper.

In In practice, it has been shown that despite an additional etching process cost-effective is based on a base material with 17 microns or 35 micron thick laminations and this over a large area chemical etching on z. B. 4 microns to decrease in thickness. For this difference sentences are the commercially available available Spray etching equipment or Schwallätzanlagen usable. Modern horizontal running spray spraying plants are able to etch the copper layer relatively evenly.

For etching printed circuit boards in the horizontal pass is also suitable for example in the document DE 30 01 726 C2 described device. The etching liquid is dammed up as a "standing wave" between accumulation rollers.Through this flooded treatment room, the circuit boards are transported and etched.The circulation-promoted etching liquid, which flows from surge pipes or flooding pipes into the treatment room and causes turbulence there, etches the large surfaces of the printed circuit boards The aim is to reduce the thickness of the metallic surfaces as evenly as possible, but the etch rate during the wave process is smaller than in the case of spray etching.

A larger etch rate achieves the device according to the document DE 197 18 769 A1 , It is a spray etching process. The etching liquid is sprayed by means of nozzle systems to the surface of the goods. As the speed and amount of etching liquids impinging on the surfaces increase, the etch rate increases. To prevent puddling transport rollers are provided with helical grooves, which dissipate the etching liquid to the side. Areas where puddles remain would result in a lower etch rate, that is, the thickness of the etched films would be uneven. This must be avoided, at least in the useful range of the circuit boards. The edges are cut off and discarded at the end of the circuit board production. Nevertheless, the thickness of the etched surface in the edge region is critical for further processes. Due to the outflow of the medium over the edges, in practice the layer in the edge areas is often thinner by approx. 1 to 2 μm than in the working area. This edge region is required in the subsequent electrolytic treatment of the printed circuit boards for electrical contacting, that is to say for the introduction of current. The edge must be able to absorb and distribute the treatment stream without overloading the stream.

The publication DE 43 01 742 C2 describes the transfer of the treatment stream from a bath source to the estate by means of rotating contact rollers in a continuous system with horizontal transport of the goods. The contact rollers form a track on the edge of the goods on which they roll.

The electrical contacting of good in the pass along an edge track also describes the publication DE 196 28 784 A1 , Contact discs with contact sectors form the contact means that roll on the estate.

Also the publication EP 0 578 699 B1 describes contact wheels that roll on the surface in the edge region of the goods.

The publication DE 36 24 481 C2 describes a further electrical contact of goods in a continuous system. By means of circulating brackets, which are in electrical connection with a Badstromquelle, the good is seized on the edge. In this case, the current at each clip is punctiform fed into the edge of the circuit board. The distance from clamp to clamp in the transport direction determines the number of contact points over which the current reaches the material.

Similar Clamps are used in immersion baths on goods carriers or on means of transport used in continuous systems with vertical transport of the goods. Again, the good is seized on the edge. The bath stream is over this Staples introduced into the edge area of the goods and from there over the surfaces distributed.

In the electrolytic treatment of printed circuit boards must be worked for reasons of economy with the highest possible current density. So come z. For reverse pulse plating current densities for the forward current of up to 15 A / dm ² and for the reverse current of up to 50 A / dm ² before. This results in a correspondingly high current per contact means, in particular with printed circuit boards with a large dimension transverse to the transport direction. Effective currents of 100 amps per contact occur in practice. This current first reaches an edge region of the printed circuit board and from there into the useful region thereof. If the metal foil in the edge region is thin, then it has a correspondingly high electrical resistance. This even if it is an electrically good conductive copper foil. Joule heat can be used to heat the brim to burns that damage the material and possibly also the contact materials. This is the case, in particular, when using a high current density only a few contact means are used for power transmission to the estate. In practice, distances of the contact means in the transport direction of the goods from 50 mm to 200 mm before. Large distances and the resulting high currents through the individual contacts can, especially when using the Pulstechnik, lead to the aforementioned errors.

Because the contact means themselves act as diaphragms and as so-called current catchers, the material is much less galvanized at this contacting edge. That's why also the current density as treatment progresses in a continuous plating plant do not increase significantly. In the practice of fine circuit board technology The thickness of the copper cladding limits the height of the maximum applicable current density. This is a big one economic disadvantage. For reasons of quality, however the thickness of the copper lining can not be increased. According to the state of Technology is only a compromise possible here.

The object of the present invention is to provide a method and a device which make it possible to etch the surfaces of planar material, in particular of printed circuit boards, in such a way that it is also used when using high current densities and high current load in the subsequent electrolytic treatment the contact means to no damage to the goods and the contact means comes. The problem is solved by the method according to claims 1 to 9 and by the device according to claims 10 to 18.

The invention is based on an etching process which treats the surfaces to be etched with two different etching rates, that is to say with a different etching rate. The edge of the material to be used in subsequent elektrolyti rule processes for making electrical contact, is etched by restricting the etching rate less than the remaining surface of the material. This larger remaining layer thickness of the Kontaktierungsrandes can absorb a significantly larger current in galvanizing and distribute in comparison to the layer thickness of the remaining surface. There is no thermal damage to the goods and / or the contact means. The different etching rates are set in the etching system by means of inserted diaphragms or covering rollers. This will be described below with reference to the schematic and not to scale 1 to 5 described in detail.

1a shows in cross section a coated on both sides with a metal foil printed circuit board before the Differenzätzen.

1b shows in cross section a finished etched circuit board according to the prior art.

1c shows an electrical contact of the etched circuit board according to the prior art.

2a shows in cross section a circuit board before the Differenzätzen.

2 B shows the finished etched circuit board according to the invention.

2c & 2d show the electrical contact of the inventively etched circuit board.

3 shows printed circuit boards in a spray etching in cross-section and in plan view.

4 shows printed circuit boards in a Schwallätzanlage in cross-section and in plan view.

5 shows a Schwallätzanlage in the side view.

In 1a is the circuit board 1 from a basic body 3 , on both sides of a metal foil 2 is laminated. The main body, which is also referred to as core, consists of an electrically insulating material, for. B. from an epoxy reinforced with glass fibers. The metal foils are usually made of copper in printed circuit board technology. The most used and most cost effective thickness of the films is 17 μm. Also 35 micron thick films occur.

These metal foils are etched in the prior art to the thickness required for the fine conductor technique. This shows the 1b , The thickness of the etched foil 4 is in practice 4 up to 5 μm. Other thicknesses occur. In-line etching uses precision etching equipment. The one with the reference number 5 designated contact edge has the width a. About this edge is in the subsequent electrolytic treatment of the required power 1 initiated into the estate. This shows the 1c using the example of double-sided contact rollers 6 that are on the contacting edge 5 roll. In place of the contact rolls 6 It is also possible to use clamps which hold the goods at the contacting edge 5 take and the electricity 1 initiate. Because the etched foil 4 is thin, it comes in a punctiform or linear current introduction via the contact means at the contact points in consequence of the increased electrical resistance to local warming. This limits the amount of current to be transmitted without error 1 , For structural reasons or cost reasons, the number of contact means, based on a unit length in the transport direction can not be increased significantly. In practice, films with a thickness of about 8 microns or larger are required to galvanize the estate with economic flows. However, this is too thick for the fine conductor technology.

The 2 shows according to the present invention, a very cost-effective solution of the requirements described above. 2a again shows the both sides to be etched circuit board 1 , The 2 B shows the finished etched circuit board. It can be seen that the contacting edge 5 was etched much less than the rest of the film 4 , During galvanizing, this thicker contacting edge can absorb a larger current from the contact elements, which are usually punctiform, and distribute them in the transport direction of the material. The thickness of the Kontaktierungsrandes should be at least 6 microns, preferably 10 microns or more to apply high current densities during plating. The 2e shows as an example a contact chamber 7 that the stream 1 in the region of the contacting edge 5 about the contact points 8th initiates both sides of the estate. Due to the thicker contacting edge, no damage to the material and the contact means occurs even when high current densities are used. The upper limit for the maximum current to be transmitted 1 no longer determines the thickness of the film here 4 but the chemical and hydrodynamic parameters of the electrolytic cell.

Because according to the invention No additional Process or materials for etching are required, the difference etching with different etching rate proves to be a very economical process for the entire process of PCB manufacturing. Also the necessary structural additions of existing etching equipment require only a little effort. This will be on the basis of the following Figures described.

The 3 shows a Sprühätzanlage for two-sided etching of the surfaces. Transverse to the transport direction of the continuous system are spray registers 9 arranged. These can consist of tubes with holes or nozzles. They can be arranged stationary or moved in an oscillating manner. The etching liquid is circulated by means not shown pumps through the spray registers 9 sprayed on the surfaces of the goods. The estate is etched. In the area of the later required Kontaktierungsrandes 5 there are diaphragms 10 , They cover the edge so that the etching liquid does not directly reach the surface of the material. This reduces the etching rate. If during the entire passage of the goods through the etching of this contacting edge 5 is covered, then the etching rate goes to zero. With the length c of the apertures in the transport direction in relation to the total active length of the etching system, the thickness of the remaining contacting edge 5 be determined. The length of the covers 10 is set stationarily in the etching system or it is made adjustable so that the etching rate can be varied depending on the respective material. With decreasing distance b of the diaphragm from the material, the transition region from the contacting edge to the useful region of the material becomes smaller. The edge is sharper and the etch rate decreases in this covered area.

The width a of the contacting edge to be realized determines the transport path of the goods in the continuous system. The transverse to the transport line tion preferably stationary arranged panels on the one hand and immersion depth of the goods in these panels along the transport path on the other hand, determine the width a of the contacting edge 5 , The immersion depth is specified by loading the etching system with good at the appropriate position transverse to the transport direction. Also, the alignment of the material in front of the etching in the required transport path by means of a mechanical positioning unit is possible.

The 4 shows another etching system. Here, the etching takes place in a not shown flooded working chamber below the level 11 the etching liquid. The reduction of the etching rate is done by capping rollers 12 that are on the less caustic edge 5 roll. With decreasing distance d of the cover rollers 12 the etch rate decreases from each other. Likewise with increasing number of rollers per unit length in the transport direction of the goods. The immersion depth of the goods in these rolls 12 again determines the width a of the Kontaktierungsrandes 5 , Cover rollers are also used in spray etchers to achieve a thicker edge 5 applicable.

The 5 shows in side view further details of the etching system according to the 4 , In a flooding tub 13 becomes the etching liquid 14 accumulated to a "standing wave" 15 prevent leakage of the flooding trough 13 in the workspace 18 , As a rule, these are jam rollers 15 driven and they also take over the function of transport rollers for the good 1 , The etching liquid 14 is by means of a pump 16 through flood pipes 17 in the workspace 18 the flooding tub 13 promoted in the cycle. The return to the pump sump 19 takes place via overflows, not shown. The cover rollers 12 can be powered or not powered. They are arranged in this example to set the required etch rate at different distances from each other. The good 1 is in horizontal pass through the workspace 18 promoted and on both sides, that is etched less at the top and bottom of the contacting edge than in the remaining area of the surface.

Basically also an etching system with cover rollers in combination with apertures to reduce the etching rate at Contacting edge possible. This extends the possibilities for influencing the layer thickness in the edge region of the printed circuit boards.

The invention is also suitable for etching in continuous systems with vertical transport of the goods. In this case, the arrangement of 5 to see rotated 90 degrees. The estate is gripped by clips on the edge and conveyed by the etching plant. The upper or lower edge is covered by apertures so that it is etched less than the rest of the good. It is later used as a contacting edge in the electrolytic treatment.

To increase the etching rate both in the region of the contacting edge 5 as well as in the rest of the estate 1 can be an injector 20 be used. By means of this injector 20 is pressurized a gas, preferably air, in the pressure line of the pump 16 and thus introduced into the etching liquid. The injection of gas into the etchant can also be used in the spray etch process to increase the etch rate.

1

PCB, Well

2

metal foil before etching

3

Basic body, core

4

etched foil

5

Kontaktierungsrand

6

Contact role

7

contact clip

8th

Contact points

9

Sprühregister

10

Cover, cover

11

level

12

covering roller

13

flooding tub

14

etchant

15

jam roll

16

pump

17

flooding pipe

18

Workspace

19

sump

20

injector

21

transport direction of the good

Claims (18)

Process for the differential etching of plate-shaped material with metal foils laminated on one or both sides, in particular of printed circuit boards and conductor foils, in etching systems with horizontal or vertical transport of the material in the passage, characterized in that by means in the etching system, the etching rate in an edge region of the material to be etched so is reduced, that this area remains larger in etching than in the remaining area of the material during etching. Method according to claim 1, characterized in that that reducing the etching rate by restriction the etching attack the etching liquid on the estate with media as screens, covers, cover rollers or Cover strips only takes place in the edge area, which later becomes electrical Contacting the goods should be used. A method according to claim 1 or 2, characterized characterized in that the thickness of the less to be etched Kontaktierungsrandes is controlled by screens or covers with adjustable aperture. Method according to claim 1 or 2, characterized that the thickness of the less corrosive Contacting edge by the number of covering rollers per unit length is set in the transport direction. Method according to one of claims 1 to 4, characterized that the width a of the less to be etched Kontaktierungsrandes by choosing the transport path of the goods among the installed Covers and cover rollers is set. Method according to one of claims 1 to 5, characterized that difference sentences with a deviating in the thickness contacting edge from the remaining area of the product by the application of a spray etch or a swell etch process he follows. Method according to one of claims 1 to 6, characterized that during etching by injecting gas into the discharge line of the etching fluid pump the etching accelerated both at the contacting edge as well as in the working area becomes. Method according to one of claims 1 to 7, characterized that the limited etching means the covers, panels and / or covering rollers in the region of the contacting edge the top and bottom of the good. Method according to one of claims 1 to 8, characterized that the estate at the entrance of the etching device Positioned transversely to the transport direction so that the thicker Contact edge is etched with the required width a. Apparatus for differential etching of plate-shaped material with metal foils laminated on one or both sides, in particular of printed circuit boards and conductor foils, in horizontal etching systems or vertical transport of the good in the pass and to the application of the method according to any one of claims 1 to 9 by means for reducing the etching rate in an edge region of the good the rest Area of the good. Apparatus according to claim 10, characterized by Means as screens or cover strips, which are close to the surfaces of the Good are arranged where the goods are less etched should. Apparatus according to claim 10 or 11, characterized by panels and cover strips, in the transport direction of the goods in length changed can be. Apparatus according to claim 10, characterized by Means as cover rollers, which roll on the edge of the good, the less etched shall be. Apparatus according to claim 10 or 13, characterized by covering rollers, which in number and / or at a distance from each other changed can be. Device according to one of claims 10 to 14, characterized by a straightening device, which is arranged in front of the etching device, for positioning the material in the of the panels or covering rollers predetermined transport path. Device according to one of claims 10 to 15, characterized through an etching system with flooding tubes in the working area, which are transverse to the transport direction are arranged and with cover rollers under bathroom mirror, which on the less too corrosive edge unroll the goods. Device according to one of claims 10 to 16, characterized through an etching system with spray sticks that are preferably arranged transversely to the transport direction of the goods and through panels or cover strips, which are between the estate and the spray sticks in the area of the transport path are arranged, in which the good less etched shall be. Device according to one of claims 10 to 17, characterized by an injector for introducing gas into the etching liquid.