WO1999030541A1

WO1999030541A1 - Printed circuits and method for making

Info

Publication number: WO1999030541A1
Application number: PCT/US1998/025395
Authority: WO
Inventors: Rodolfo Kroebel Nieto
Original assignee: Lear Automotive Dearborn, Inc.
Priority date: 1997-12-05
Filing date: 1998-11-30
Publication date: 1999-06-17
Also published as: KR20010015829A; EP0923278A1; JP2002503878A

Abstract

A printed circuit manufacturing process for making a two-sided circuit includes starting with two pieces of conductive material (10) such as copper. One side (11) of each piece of the conductive material is chemically machined or cut to form grooves (13) corresponding to the desired design of the printed circuit. The two pieces (10) are then held in a desired, generally parallel alignment with a spacing between oppositely facing grooves (13). A dielectric material (14) is then injection molded onto each piece of the conductive material so that the dielectric material (14) fills the grooves (13) that have been formed in the conductive material and fills the spacing between them. The opposite sides (12) of the conductive material are then subjected to a process to form the grooves (16) that correspond to the desired printed circuit design. The grooves (16) formed during this latter step preferably are coincident with those formed in a previous chemical machining or cutting step.

Description

PRINTED CIRCUITS AND METHOD FOR MAKING

BACKGROUND OF THE INVENTION

The present invention generally relates to a manufacturing process for two-sided printed circuits that includes a machining step for shaping a design for the printed circuit and a molding step to place a dielectric layer between two sets of circuit traces.

Manufacturing processes, such as the ones disclosed in the Spanish Patent No. P9200325, which has common ownership with this application, are known. The increase in performances and therefore in the functions offered to a vehicle user requires a continuous improvement in quality, cost- effectiveness and size of the service boxes that contain the printed circuits. The size of the service box must be increased if there is a desire to follow with the practice of integrating the entirety of the printed circuits, plus the functions entrusted to the same, within a single service box.

All that has as a consequence that the space problem is most relevant. Even with the advancement in the integration of printed circuits as is disclosed in Spanish Patent No. P9501610 (having common ownership with this application), the functions and performances mentioned above are still growing, since manufacturers are increasingly offering, even in compact cars or relatively lower-cost vehicles, performances and functions that were previously offered only in top class models.

Conventional procedures for manufacturing printed circuits start basically with a dielectric support, made of epoxy resins and glass fibers or the like. A copper plate is adhered to the dielectric support and the copper plate surface is covered with an anti-acid substance. The covered copper surface is then subjected to a chemical attack. The design of the cover ensures that the desired zones form a series of conductive tracks in the copper plate. Subsequently corresponding mechanizing with inserting machines introduces the chemically treated plates between the printed circuit thus forming components of any type and, in certain cases, forming an architecture on the bases of folding the plates by methods known as shown for example in Spanish Patent No. P9200325, and/or sewing with pins, either short and/or long as is known in the art.

The improvement degree on such circuits has arrived, no doubt and in some technical aspects from the use of increasingly greater copper plate thicknesses in order to be able to support in a smaller space equal or greater intensities. That way, the same surface of the printed circuit can integrate a greater number of elements, and therefore functions, all with the above- mentioned goal of being able to keep all the printed circuits in a reduced space (t^'.e. , the service box).

The manufacturing of the tracks and therefore that of the inter-tracks and the space formed between two conductive tracks on the basis of the conventional technique {i.e. , that of the masked chemical attack) produces certain grooves, formed by vertical walls that are not perpendicular to the top surface of the copper plate. This shortcoming of the prior art is that the inter- tracks form inclined planes on the side walls producing a loss of about three percent to four percent of the conductive surface. The percentage of loss tends to increase when further copper thicknesses are used in such circuits, as disclosed for example, in Spanish Patent No. P501610 (having common ownership with this application).

As can be seen in Figure 6, with conventional methods of printed circuit manufacturing, a copper plate is adhered over a dielectric support 116. The copper plate is covered in the areas where the chemical attack is not desired. Producing the chemical attack over the copper plate results in the corresponding tracks 115 and the grooves or inter-tracks 113 having walls in the shape of inclined planes. The distance between tracks in the lower part of the grooves, where there is the interface between the copper plate with the dielectric substrate, has a smaller width than in the upper part of the same. The result of the production of the grooves 113 with inclined walls, as shown in Figure 6, is better seen in Figure 7, which illustrates how a volume

118 of the conductive track 115 is lost. The amount of volume that is lost results from the loss of material coming from the simple product of the height "d" of the material by the width "c" by the length of the track 115.

It is therefore desirable to provide a printed circuit manufacturing process that meets the needs of modern systems while avoiding the shortcomings and drawbacks of the prior art described above.

This invention includes an improvement over that shown in Spanish Application No. 9700184 (commonly owned with this application). The improved method and assembly of this invention provides enhanced manufacturing economies and a more reliable and less expensive end product.

SUMMARY OF THE INVENTION

In general terms, this invention is a manufacturing process for making two-sided printed circuit boards. The process begins with taking a copper plate and machining grooves into the plate in accordance with the desired design of the printed circuit. A second copper plate is treated in the same manner. The two treated copper plates are then placed in a generally parallel alignment. A dielectric material is then molded onto the conductive plates so that the dielectric material fills the spacing between the plates and the grooves that have been machined on each plate. This results in an assembly of the dielectric in a middle portion with the conductive material on either side. The exposed conductive material preferably is then subjected to one of three processes to form grooves that coincide with the grooves that were previously machined. The three processes can include a conventional chemical attack, chemical machining or chemical cutting. The process results in tracks and grooves on both sides of the assembly having better geometric characteristics than those accomplished with the prior art. The object of the present invention is that of introducing a new way of manufacturing printed circuits, in order to be able to absorb the losses of the three percent or four percent that happen when manufacturing printed circuits with traditional methods. Further, this invention simplifies the manufacturing of printed circuits on the base of grouping a series of operations in a single assembly. This allows some of the manufacturing operations to be performed in the plant of the printed circuit manufacturer itself. Moreover, this invention greatly simplifies the process of making a two-sided circuit board. Further, this invention eliminates the need for the techniques of forming a negative of the desired configuration and then later using a chemical attack. Therefore, this invention provides a gain in manufacturing speed and utilizes processes with no adverse consequences for the environment.

Other details and characteristics of the invention will be manifest through the reading of the detailed description given below, in which reference is made to the figures attached to the description. These details are given as an example, referring to a case of a practical embodiment, that is not limited to the details outlined. Therefore the following description must be considered from an illustrative point of view and with no limitations whatsoever.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an elevational, cross-sectional view of a conventional copper plate useful for printed circuit manufacturing.

Figure 2 illustrates the plate of Figure 1 after it has been subjected to a chemical machining or chemical cutting process.

Figure 3 is an elevational, cross-sectional view of the embodiment of Figure 2 with an injection molded dielectric substrate attached. Figure 4 is an elevational, cross-sectional view of the embodiment of Figure 3 later in the inventive process.

Figure 5 shows another embodiment where two products made as shown in Figure 4 are joined together. Figure 6 illustrates the state of the art.

Figure 7 is an enlargement of the circled portion of Figure 6.

Figure 8 illustrates the preferred method of making a two-sided circuit board at an early stage in the process.

Figure 9 shows the embodiment of Figure 8 at a later stage in the process.

Figure 10 illustrates a finished product made using the preferred method of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The operations integrating the printed circuit manufacturing process of this invention preferably begin with a copper plate 10 having an upper face 11 and a lower face 12. As shown in Figure 2, chemical machining or cutting is used to produce grooves or inter- tracks 13 as indicated by the arrows. Figure 2 is a schematic and illustrative illustration of one embodiment of this invention.

There follows after the chemical cutting or machining process, an injection molding process to mold a fully dielectric material or substance of a generally plastic type within the machined grooves 13. The injection molded material preferably is capable of withstanding high temperatures, since afterwards the assembly is sometimes introduced into a wave welding machine for purposes that will become apparent below. If the plastic is not of such special characteristics, it could not withstand the temperature and distortions could be produced in the printed circuit that is manufactured. The injection molding operation serves two basic purposes. First, it gives the necessary dielectric support to the printed circuit. Second, it efficiently protects the inter-tracks 13 formed in the copper plate, in which can be seen that the walls of the grooves or inter-tracks are nearly fully vertical {i.e. , perpendicular to the outside face 11 of the copper plate). The injection molded dielectric 14 also gives a certain mechanical stiffness to the assembly.

There follows the same process in the opposite face of the copper plate 10 (the lower part according to the drawing), as represented in Figure 4, preceding again to a chemical attack, chemical machining or cutting operation to form the inter-tracks or grooves 16. As can been seen in the drawing, the cross-section of the tracks 15 is practically rectangular, with the result that the loss of material or volume (118 as shown in Figure 7) does not happen, which would otherwise be the consequence of the conventional methods forming inclined planes instead of vertical ones in the inter- track walls. The embodiment of Figure 3 is subjected to the chemical attack, machining or cutting process to form the grooves 16 coincident with the grooves 13, which have previously been filled with the dielectric material 14. Any of the above three processes can be used for this step. With the circuit formed this way by this new procedure, one way that double faced circuits can be formed is shown in Figure 5. In one embodiment, the deposition of an adhesive in order to glue more than one assembly together facilitates forming a double faced circuit. The wave welding mentioned above provides a suitable method of joining two dielectric layers when the material has the desired heat-resistant characteristics.

Alternatively other joining methods can be used including sewing single circuits, by techniques such as those of short pins or long pins, as disclosed in the Spanish Patent No. P9200356 and as are known in the art.

Other conductive material plates of conductive characteristics similar to those of copper can be used. A variety of substances with dielectric properties can be used and in some instances preferably include the above- mentioned characteristics of being able to withstand high temperature and being able to be used easily in an injection molding process in order to penetrate between the inter-tracks 13. The dielectric can be treated with a glue or adhesive in order to form double circuits as shown in Figure 5.

Temperature resistant properties of the dielectric 14 preferably accommodate a molding process for joining two assemblies.

Further to the above-mentioned advantages of this new method of circuit manufacturing, a better insulation of the inter-tracks 13 is achieved because of the easiness of the molding injection operation in order to be able to produce a higher or lower pressure over the material to be injected, as well as choosing the most appropriate nature of the same, such as flow, density, etc. Further, no later protection of the inter-tracks 13 with varnish is required. Alternatively and on the same inventive idea, the molding operation may be substituted with the application of a simple coating of the base 11 after the grooves 13 have been formed in its surface, refilling the grooves 13 with any material of dielectric nature. The same later steps described above preferably then are used to complete the circuit manufacturing process.

Referring now to Figure 8, the most preferred method of this invention is schematically illustrated. Upper plates 10, which have had one face treated by the chemical machining or cutting process to form the inter-tracks 13 (as shown in Figure 2) are positioned in a generally parallel alignment. A set of holding members 30 are utilized to maintain the copper plates 10 in the desired orientation with a spacing between them. Then an injection molding process preferably is utilized to inject a dielectric material 14 into the spacing between the plates 10, filling the inter-tracks 13.

The configuration resulting from the injection molding process is illustrated in Figure 9. It should be noted that other methods of molding a dielectric material 14 into the spaces between the copper plates 10 besides injection molding can be utilized in accordance with this invention. As shown by the arrows in Figure 9, the surface 12 of the copper plates is subjected to a chemical attack, machining or cutting process to form the grooves 16 coincident with the inter-tracks 13, which have been filled with the dielectric material 14. The resulting configuration having two sets of circuit tracks 15 is illustrated in Figure 10.

Accordingly, this invention provides a more efficient method of making a two-sided circuit plate with a dielectric support 14. Rather than having to adhesively secure two separate dielectric supports together or to utilize a wave welding process as described above, the embodiment of this invention diagrammatically illustrated in Figures 8 through 10 includes an additional improvement. The one-step molding process for the dielectric material 14 introduces manufacturing economies and increases the range of dielectric materials 14 that can be used as the dielectric support for a two- sided circuit. The preceding description is exemplary and not limiting. The scope of protection is only to be limited by the following claims.

Claims

CLAJTMS

The following is claimed:

1. A method of making a printed circuit, comprising the steps of:

(A) forming a plurality of channels (13) in a first face (11) of a first piece of conductive material (10) according to a desired configuration of the printed circuit;

(B) forming a plurality of channels (13) in a first face (11) of a second piece of conductive material (10); characterized by

(C) attaching a dielectric material (14) to the first face of each piece of conductive material (10) such that the dielectric (14) fills the channels (13) formed during step (A); and

(D) forming a plurality of channels (16) in a second face (12) of the first and second pieces of conductive material (10) such that the dielectric material (14) is exposed within the channels.

2. The method of Claim 1, wherein steps (A) and (B) are performed using a chemical machining process on the first face of the conductive material.

3. The method of Claim 1, wherein steps (A) and (B) are performed using a chemical cutting process.

4. The method of Claim 1, wherein steps (A) and (B) are performed using a machining process.

5. The method of Claim 1, wherein steps (A) and (B) include forming the channels through approximately one-half of a thickness of the conductive material.

6. The method of Claim 5, wherein step (D) includes forming the channels (16) through approximately one-half of the thickness of the conductive material and forming the channels of step (D) coincident with the channels (13) of steps (A) and (B).

7. The method of Claim 1, wherein steps (A), (B) and (D) are performed to form channels having a rectangular cross section.

8. The method of Claim 1 , wherein step (C) is performed by injection molding the dielectric material (14) onto the conductive material.

9. The method of Claim 1, wherein step (C) includes positioning the first and second pieces of conductive material (10) in a generally parallel alignment with a preselected spacing between the pieces of conductive material.

10. The method of Claim 9, wherein the channels (13) from steps (A) and (B) are facing each other when the pieces of conductive material (10) are aligned.

11. The method of Claim 10, wherein the dielectric material (14) is molded into the spacing between the pieces of conductive material and wherein the dielectric material fills the channels (13).

12. The method of Claim 11, wherein the dielectric material (14) is injection molded into the spacing between the pieces of conductive material (10). lS. The method of Claim 1, wherein step (D) is performed using one of a chemical etching process, a chemical cutting process or a chemical machining process.

14. A printed circuit comprising: a first piece of conductive material (10) having a plurality of channels

(13) formed in at least one surface (12) of the conductive material; a second piece of conductive material (10) aligned with and spaced from the first piece, the second piece having a plurality of channels (13) formed in at least one surface (12) of the conductive material; a dielectric material (14) molded into the space between the first and second pieces and filling the channels (13) such that a layer of dielectric material is attached to and supports each piece of conductive material.

15. The printed circuit of Claim 14, further comprising a plurality of grooves (16) formed in each piece of conductive material in alignment with the channels (13), respectively, such that opposing faces of the printed circuit each have a plurality of conductive tracks (15).

16. The printed circuit of Claim 14, wherein the dielectric material

(14) is injection molded into the space.