IES80643B2 - Production of printed circuit boards - Google Patents

Abstract

Circuits are produced using photo tool films (40). Film mounting apertures (B) are located centrally at each side of the film (41) for mounting the film in a similar manner irrespective of the particular circuit pattern. Corresponding substrate registry apertures (C) are located accurately in the film with respect to the mounting apertures (B). A pattern (44) is printed so that the registry apertures (C) are within a margin (45). A series of printed apertures (A) in the margin (45) is used for mounting of the substrate for drilling and routing as corresponding program commands are transmitted to the drilling and routing machine. Each corner of the printed margin (45) has a pair of solder mask registry marks (E), one extending in each of the X and Y directions. Each mark has a blank rectangle with a central dot and a pair of cross hairs. These are used for solder mask registration with a process control check being carried out by additional printing registry marks (D). For silk screen printing, the printing marks (D) are used for mounting and registration, and the solder mask registry marks (C) are used as a process for control checking.

Description

“Production of Printed Circuit Boards” The invention relates to the production of printed circuit boards.

As described in United States Patent Specification No. US4863550 (Somar Corp.), in such a process, circuits are applied to two external surfaces of a substrate for single layer and multi-layer boards. A photoresist layer is laminated onto each side of the substrate and this is protected in turn by a protective lamination. The photoresist is exposed through a circuit photo tool film and the resulting photoresist pattern is used for plating the circuit and subsequently etching the excess conductive layer.

Many automated processes have been developed for production of printed circuit boards in high volumes. However, these processes lack the required flexibility for production of relatively small batches with frequent batch changes such as required for prototyping.

Some work has been carried out at modifying the production process for prototyping. Such a process is described in PCT Patent Specification No. WO 89/05566 (Versatronics Ltd). This specification describes a computer system which drives a drill station. However, little information is given as to how the main circuit and solder mask applying operations are carried out.

The invention is directed towards providing a production process which allows efficient production with excellent quality for low volume production with frequent batch changes.

S δ 0 ό 4 6 -2According to the invention, there is provided a process for manufacturing a printed circuit board, the process comprising the steps of:in a computerised design system, generating:circuit photo tool film patterns, solder mask photo tool film patterns, and silk screen printing patterns, and control commands for a drilling and routing machine; drilling and routing a substrate clad with a conductive layer according to the control commands; printing outer layer photo tool circuit patterns on films having a standard base with film mounting apertures on at least two sides; mounting the outer layer photo tool films on the base of an exposure station using the mounting apertures; aligning a drilled substrate with the outer layer photo tool films by engagement with pins extending through substrate registry apertures in a printed margin surrounding the circuit pattern; exposing the circuit pattern, plating the circuit, and etching the excess conductive layer; covering each circuit with a solder mask layer, and aligning the substrate with a solder mask photo tool film using mask registry marks in the printed margin, and exposing the solder mask pattern; and -3mounting the substrate on a silk screen printing station using printing registry marks in the printed margin, and printing component information on the solder mask.

The mounting apertures of a film allow consistent and repeatable mounting of the film, and the substrate registry apertures allow consistent and accurate registration of the substrate with the film. The printed margin provides a range of marks to ensure effective registration for the subsequent solder mask exposure and silk screen printing operations. Thus, irrespective of the size of the circuit pattern on the film, the film has a consistent size, is mounted in the same way at the outer layer exposure station, and registration of the subsequent steps is carried out in the same manner using registry marks in the printed margin. This allows efficiency and excellent quality control in a consistent manner irrespective of the particular circuit pattern at any time.

Preferably, the outer layer photo tool films are rectangular and the mounting apertures are at each side of the film and are outside of the printed pattern.

In one embodiment, the registry apertures are in an L-shaped configuration at three comers of the printed margin.

In another embodiment, the registry apertures are punched independently of the printed pattern.

In one embodiment, the mask registry marks are at each comer of the printed margin.

Preferably, there are two mask registry marks at each comer, one extending in each of the orthogonal directions. -4In another embodiment, the mask registry marks include a dark spot which causes a pad to be plated, and cross-hairs.

In another embodiment, the pad and cross-hairs are within a blank enclosure and the 5 background printed margin is dark.

Preferably, the printing registry marks are used for process control checking for registry of the solder mask photo tool film.

In one embodiment, the printing registry marks comprise concentric patterns.

In one embodiment, the solder mask registry marks are used for process control checking for registry of the silk screen.

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which:Figs. 1 and 2 are together a flow diagram illustrating a production process of the invention; Fig. 3 is a representation of an outer layer photo tool film used in the process: and Fig. 4 is an exploded view of part of the film of Fig. 3 showing registry marks in more detail.

Referring to the drawings, there is illustrated a production process 1 for production of a circuit board. The circuit board may be of the single-layer or multi-layer type. A computer aided design system 10 is used in the process, together with drilling and -5routing machines, circuit exposure stations, copper plating and etchings stations, solder mask exposure stations, and silk screen printing stations.

The computer aided design (CAD) system 10 prints photo tool films in step 11. Silk 5 screen printing photo tool films are used for production of silk screen printing films in step 12. Before describing the remainder of the process, a photo tool film 40 is now described with reference to Figs. 3 and 4. The film 40 is an outer layer circuit photo tool film which comprises a transparent plastics film 41 having an un-printed portion 42 forming a narrow margin and a larger un-printed portion 43. The printed portion is indicated generally by the numeral 44 and it comprises a dark printed margin 45 surrounding circuit patterns. The circuit patterns comprise a dummy pattern 46 which is not used for circuit printing, and five circuit patterns 47. The circuit patterns 47 are arranged by the system 10 to achieve optimum use of the circuit surface area.

The film 41 has a set of four mounting apertures B, one located centrally adjacent each side edge. These apertures are punched independently of the printed pattern 44. The remainder of the marks used in the production process are located in the printed margin 45. These include a series of apertures A which that are not physically punched in the film, but are printed. These apertures are embedded in the commands transmitted to the drill and routing machine. They are used to drill holes in a copper clad substrate so that it can be mounted accurately for subsequent drilling and routing operations.

There are also three substrate registry apertures C in an L-shaped configuration at three comers of the printed margin 45. These apertures are physically punched in the film. -6A printing registry mark D is located at each comer of the margin 45. It comprises a dot and a “concentric” square around the dot. These marks are only printed on the margin. In addition, there is a pair of solder mask registry marks E at each comer of the printed margin 45. Each mark E comprises a blank rectangular box (the printed margin background is black) in which there is a centrally-located dot which causes a pad to be printed at the corresponding location on the circuit, and a pair of crosshairs on each side of the dot.

The manner in which these marks are used is now described in more detail with 10 reference to the flow diagram of Figs. 1 and 2.

In step 14 a Cu-clad substrate is mounted using the apertures A at a drill and routing machine. At this position, the drill and routing machine uses program commands from the system 10 to drill and rout the substrate. The drilling is for the through15 holes and the routing is for various indentations in the substrate required by the circuit design.

In step 16 photoresist is applied to both surfaces of the substrate and the photoresist is protected by a MYLAR ™ protective film.

To expose the circuit patterns onto the photoresist layer, a pair of outer layer photo tool films are mounted at an exposure station. The films are mounted by engagement of the mounting apertures B with corresponding pins in the glass base of the exposure station. The film 41 is a consistent size and the mounting apertures B are located at the same location and thus, this operation is the same irrespective of the printed circuit pattern. This allows consistency with high-quality despite the fact that there may be frequent batch changes. When the outer layer photo films have been mounted, in step 18 the Cu-clad substrate is placed in registry with the films by engagement with pins extending through the registry apertures C. As described above, the apertures C are physically punched in the film 41 and are accurately -Ί located with respect to the mounting apertures B. Thus, the apertures B and C are located for film mounting and the printed pattern 44 is located so that the registry apertures C are within the printed margin 45.

To ensure accurate registration, a process control check is carried out in step 21 using the printing registry marks D. These marks are particularly effective for visual inspection because non-alignment will be immediately apparent because a dot is located at the centre of the outer square part of the mark. In step 19 the circuit pattern is exposed according to the registry achieved in steps 17, 18, and 21, and in step 20 the circuit is plated and etched in a conventional manner.

The outer surfaces of the substrate are covered with a solder mask lamination in step 22 and in step 23 a pair of solder mask photo tool films are aligned with the outer surfaces using the solder mask registry marks E. This is a very accurate registration because of use of the dots and cross hairs extending in each of the X and Y directions at each of the four comers of the printed margin 45. An additional check to ensure accurate registration is achieved by checking alignment of the printing registry marks D.

The solder mask pattern is exposed in step 25 and the solder mask is then removed using conventional techniques to expose the circuit pads.

In step 26, the substrate is mounted for silk screen printing using the registry marks D, and a process control check is carried out in step 27 using the solder mask registry marks E.

The component identifier information is printed in a silk screen printed path in step 28, and there is a final visual inspection in step 29. -8It will be appreciated that the arrangement of film and printed pattern allow for accurate registration throughout the process in a consistent manner irrespective of the printing pattern. This allows both efficiency and excellent quality control for low-volume batches with frequent changes.

The invention is not limited to the embodiments described, but may be varied in construction and detail within the scope of the claims.

Claims (5)

Claims

1. A process for manufacturing a printed circuit board, the process comprising the steps of:5 in a computerised design system, generating:circuit photo tool film patterns, solder mask photo tool film patterns, and silk screen printing patterns, and control commands for a drilling and routing machine; drilling and routing a substrate clad with a conductive layer according to the control commands; printing outer layer photo tool circuit patterns on films having a standard base with film mounting apertures on at least two sides; mounting the outer layer photo tool films on the base of an exposure station 20 using the mounting apertures; aligning a drilled substrate with the outer layer photo tool films by engagement with pins extending through substrate registry apertures in a printed margin surrounding the circuit pattern; exposing the circuit pattern, plating the circuit, and etching the excess conductive layer; -10covering each circuit with a solder mask layer, and aligning the substrate with a solder mask photo tool film using mask registry marks in the printed margin, and exposing the solder mask pattern; and 5 mounting the substrate on a silk screen printing station using printing registry marks in the printed margin, and printing component information on the solder mask.

2. A process as claimed in claim 1, wherein the outer layer photo tool films are 10 rectangular and the mounting apertures are at each side of the film and are outside of the printed pattern, and wherein the registry apertures are in an Lshaped configuration at three comers of the printed margin, and wherein the registry apertures are punched independently of the printed pattern,and wherein the mask registry marks are at each comer of the printed margin, and 15 wherein there are two mask registry marks at each comer, one extending in each of the orthogonal directions, and wherein the mask registry marks include a dark spot which causes a pad to be plated, and cross-hairs, and wherein the pad and cross-hairs are within a blank enclosure and the background printed margin is dark.

3. A process as claimed in any preceding claim, wherein the printing registry marks are used for process control checking for registry of the solder mask photo tool film, and wherein the printing registry marks comprise concentric patterns, and wherein the solder mask registry marks are used for process 25 control checking for registry of the silk screen.

4. A process substantially as described with reference to the drawings.

5. A circuit whenever produced by a process as claimed in any preceding claim.