GB2197132A

GB2197132A - Making metal-core printed circuit boards

Info

Publication number: GB2197132A
Application number: GB08720758A
Authority: GB
Inventors: Helmut Karla
Original assignee: Kollmorgen Corp
Current assignee: Kollmorgen Corp
Priority date: 1986-09-16
Filing date: 1987-09-03
Publication date: 1988-05-11
Anticipated expiration: 2007-09-03
Also published as: GB8720758D0; DE3631426A1; GB2197132B; DE3631426C2; EP0260483A2; EP0260483A3; JPS6377195A

Description

SPECIFICATION Metal-core printed circuit boards and process for making same The invention relates to a process for the manufacture of metal-core printed circuit boards.

It has already been suggested to manufacture such boards by providing holes in the metal core and laminating prepregs on both sides of the metal core, simultaneously filling the holes with epoxy resin, and subsequently providing a second set of holes with a smaller diameter so that a layer of insulating material is retained on the hole walls, and metallizing the same.

Up to the date of this invention, it has not been possible to ensure that the holes were completely filled with insulating material and free of air pockets. Under unfavorable conditions, such incomplete filling or air pockets may result in defects in the hole wall insulation and short-circuits between the metal core and the hole wall metallization; or to weak points which might cause failure in future operation.

It is the object of the invention to ensure complete filling of the holes free of air pockets, and thereby to produce metal-core printed circuit boards of reliable quality. This is espe cialiy important since such printed circuit boards are used in fields of application where high reliability of operation is an absolute prerequisite. The metal-core printed circuit board in correspondence to the invention is characterized by a groove pattern on at least one side of the metal core. The groove pattern is preferably arranged in such manner that each hole on its circumference is connected to a number of grooves.

The process for the manufacture of such metai-core printed circuit boards comprises the steps of providing the metal core with a first set of holes; filling said first set of holes with insulating material simultaneously providing the surface of the metal core with an insulating layer; providing said holes filled with insulating material with a second set of holes, said second holes having a smaller diameter than the first holes, thus retaining a layer of insulating material on the walls of said first holes, characterized in that at least one side of the metal plate forming the metal core is first provided with a pattern of grooves or channels, and subsequently the first set of holes is produced; and that the thus prepared metal core is provided with the insulating layer in a press-laminating step with said grooves or channels serving as air-vents thus causing that the holes are completely filled with insulating material free of air-pockets; and that in a later process step the second set of holes is produced.

It has been found to be preferable to choose the distance between adjacent grooves so that the first holes are connected along their periphery to a number of grooves.

In accordance with one embodiment of the invention, the grooves are arranged in a gridlike pattern. In a preferred embodiment the surface of the metal core is laminated under heat and pressure simultaneously filling the first set of holes with insulating material while the air escapes via the grooves.

In one embodiment of the inventive process, the or one of the grooved surface(s) of the metal core and the other side is (are) covered by a prepreg in a laminating process using heat and pressure, thus simultaneously filling the holes with the epoxy resin. The air from the holes escapes via the grooves on the side covered with the metal sheet. Subsequently, a prepreg is laminated on the second side of the metal core.

The invention is described in more detail in connection with the attached drawings.

Fig. 1a shows the metal core provided with a network of grooves or channels.

Fig. 1b indicates the preferred dimensions of the grooves and the interspaces between them. The width of the grooves arranged in an orthogonal pattern is 0.2 mm and the distance between two adjacent grooves is 0.8 mm. The depth of the grooves may be 0.035 mm.

Fig. 2 shows the metal-core plate provided with said grooves (as shown in Fig. 1a) with a slot-shaped hole connected to a number of grooves.

Fig. 3 shows a cross section of a cylindrical hole through the metal core with the groove pattern.

The grooves might be produced by etching.

In order to do this, a photoresist mask is printed on the metal-core board and subsequently the grooves are formed by etching; finally, the etching mask is removed.

The groove pattern can also be produced by coining or any other known method.

Exemplary, the inventive process may comprise the following steps: (1) cutting the aluminum metal-core sheet to the specified size; (2) cleaning the surfaces and applying a dryfilm photoresist (RistonB 3315) on both sides; (3) exposing the photoresist layer through a negative mask of the groove pattern, developing and thereby forming the photoresist etching mask; (4) etching the exposed metal surface with copper(ll)-chloride to a depth of 0.035 mm; (5) stripping of the mask; (6) drilling holes corresponding to the hole pattern with the drill entering from the unetched side of the metal core and the diameter of the drill corresponding to the specified hole diameter plus 0.4 mm; (7) deburring with a copper(ll)-chloride solution; (8) Laminating epoxy prepregs and copper foil first from the side having no grooves and subsequently from the other side; (9) drilling second set of holes with the specified diameter; (10) cleaning the holes and continuing treatment as known for two-sided printed circuit boards, Process step (8) is performed according to Figs. 4a and 4b showing the arrangement of the metal core, the pressure plates, the prepregs and the copper foil.

The aluminum metal core may be substituted by other suitable metals such as iron, copper and copper-lnvarcopper laminates.

A further advantage of the claimed process is that by using the grooved metal core, heat transfer is improved between the insulating material and the metal core.

Claims

1. Process for the manufacture of metalcore printed circuit boards comprising the steps of providing the metal core with a first set of holes; filling said first set of holes with insulating material simultaneously providing the surface of the metal core with an insulating layer; providing said holes filled with insulating material with a second set of holes, said second holes having a smaller diameter than the first holes, thus retaining a layer of insulating material on the walls of said first holes, characterized in that at least one side of the metal plate forming the metal more is first provided with a pattern of grooves or channels, and subsequently the first set of holes is produced; and that the thus prepared metal core Is provided with the insulating layer in a press-laminating step with the said grooves or channels serving as air-vents thus causing that the holes are completely filled with insulating material free of air-pockets; and that in a later process step the second set of holes is produced.

2. The process of claim 1 characterized in that the said groove pattern is grid-like and that the distance between the single grooves is selected so that each hole is connected to a number of grooves.

3. The process of claims 1 and 2 characterized in that the grooves have a depth of 0.035 mm and a width of 0.2 mm, and that the distance between the edges of the grooves Is 0.8 mm.

4. The process of claims 1 and 2 characterized in that the grooves are produced by a process comprising printing a photo-resist mask and etching.

5. The process of claims 1 to 4, characterized in that the insulating layer is applied by laminating prepreg material.

6. The process of claims 1 to 5, characterized in that the first side of the metal core and the first set of holes are provided with an insulating layer, and that, in a later step, the second side is provided with such layer.

7. The process of claim 6, characterized in that for the press-lamination step, one side of the metal core is provided with a removable metal sheet or plate and the other side with an insulating layer material in sheet form, and that the latter is laminated onto the metal core using heat and pressure in a well-known manner, at the same time filling the holes with insulating material provided by said insulating layer sheet.

8. The process of claim 7, characterized in that subsequently the second side of the metal core is coated with insulating material in a well-known manner.

9. The process of claims 1 to 8, characterized in that the insulated hole walls are subsequently metallized in a well-known manner.

10. A metal-core printed circuit board provided with holes, characterized in that the metal core is provided with a groove pattern.

11. The circuit board of claim 10, charaterized in that the outer circumference of the holes is connected to a plurality of grooves.

12. The printed circuit board of claims 10 and 11, characterized in that the grooves are filled with insulating material.