JPS6059799A - Composite layer printed circuit board and method of producing same - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a printed circuit board, and more particularly, to a method for removing components,
It relates to a printed circuit board that is easy to replace.

It is common practice to attach complex electronic implants to printed circuit boards by passing the component pins through plated holes in the printed circuit board and soldering them in place.

Plated through holes typically connect pins and conductive materials forming part of the circuit at various levels of the circuit board.

If a component needs to be removed, for example if it has failed and needs to be replaced, the heat used to melt the solder will tend to cause the printed circuit board to expand and damage the circuitry. I know. This problem is particularly severe for very large scale integrated circuit components mounted in so-called pin grid array packages.

In the case of a large number of closely packed pins in an array (usually 100 or more), the solder on all the pins must be melted at the same time to avoid an unduly long operation. The large amount of heat thus applied and the relatively large thickness of the printed circuit board due to the large number of connections that need to be made further exacerbate the expansion problem and increase the loss i of the printed circuit board. Moreover, due to the high cost of these components, it is desirable in every respect to repair the printed circuit board rather than discard it.

In fact, it has been suggested that the only way to solve this problem is to use sockets soldered to printed circuit boards. The components are fitted into sockets, which increases the cost and bulk of the printed circuit board, and reduces reliability and electrical performance.

The present invention is a multilayer printed circuit board comprising alternating layers of epoxy glass and conductive material, a polyimide glass layer on one side of the printed circuit board, and an outer surface of the polyimide glass layer. conductive pads adapted to connect to component connection pins, arranged and arranged to reduce the possibility of damage to the printed circuit board during removal or replacement of installed components; To provide a printed circuit board characterized by:

The present invention also provides a method of manufacturing a multilayer printed circuit board assembly comprising a polyimide layer having a plurality of epoxy glass layers supporting conductive portions and a conductive area including conductive pads on the outer surface. bonding the top layer of glass to each other to form a stack, placing components with connecting pins on the printed circuit board and engaging at least some of the connecting pins with the conductive pads; A method is provided, characterized in that it consists of soldering a pin to a pad.

Preferably, a substantially complete layer of conductive material extends between the polyimide glass layer and the adjacent epoxy glass layer.

Preferably, the polyimide glass and epoxy glass layers are hand-sanded and joined by completing the curing of a sheet of prepreg sandwiched between the layers. One prepreg sheet is adjacent to the nearly complete layer of conductive material.

Hereinafter, a printed circuit board constructed according to the present invention will be described in more detail with reference to the accompanying drawings.

Referring to FIGS. 1 and 2, a printed circuit board, generally designated by the reference numeral 1, is shown supporting a component 2. Referring to FIGS. This component 2 has a large number of pins (for example 13
5 or 179 pin grid array packages. Only one of these pins is designated 3.

The printed circuit board 1 is a multilayer board (the front layer is not shown), using conductive materials in the inner layers interconnected by plated through holes, as is well known. Such a through hole is indicated at 4 and has a plated portion 5.

The internal layer may be a voltage (ie, ground or power) plane or a signal plane.

Plane 6 is an example of a voltage plane, which consists of a nearly uniform layer of conductive material, in contact with some through holes, but with holes drilled to allow other objects to pass through without making contact. It is. The signal plane includes various conductive tracks, for example track 7 is shown here as an example in contact with plating 5 of hole 4. It will be appreciated that many other layers may be provided on the circuit board supporting the pin grid array package.

Plated through holes such as hole 4 do not support component pins. Instead, these pins can be inserted into holes such as hole 8,
In the figure, it is supported by a hole that supports pin 3. The inner walls of these holes are not plated.

The opening of the hole 8 on the side of the printed circuit board 1 opposite the component 2 is surrounded by a pad 9. The pad 9 is connected to the NO hood 1 by a surface track 10, which pad 11 surrounds the opening of the hole 4 and is connected to the plating 5 thereof. In this embodiment, each of the other unplated holes similarly connects to a plated through hole.

A solder resistant layer 12 is provided over all of the plated through holes, but leaves pad 9 and all other pads around the non-plated holes exposed.

Most printed circuit boards are constructed of epoxy glass with a conductive layer. The boundary of the epoxy glass is a voltage plane 6, and on the opposite side there is a polyimide glass layer 13.
To install the component, insert its pin into the unplated hole and tin the surface containing pad 9 and similar pads.
Move against the lead solder wave, leaving a solder fillet 14 connecting pad 9 to pin 3. This fillet similarly connects other pins to the printed circuit board.

Solder never penetrates into non-plated holes, and solder-resistant layer 1
2, it does not enter the plating through hole. This solder resistor Ml,2 also acts as a thermal barrier.

If you want to remove the components, you can remove the printed circuit board with tin.
Suspend above the lead solder wave, melt the solder on all pins of this component, and remove this component. Then, gently blow away the solder that spans the holes, and then use warm air to solidify it. After drilling the holes, insert the replacement part and solder it in place. Components in a given position can be changed as many times as needed. In this way, printed circuit boards can be repaired or modified economically and easily.

It has been found that it takes 3 to 5 seconds to melt the solder and remove the pin grid array package, with negligible damage to the printed circuit board. This is comparable to soldering package pins to plated through holes in a printed circuit board constructed entirely of epoxy glass as an insulator. It is known that it takes several tens of seconds to melt the solder, and even if the solder on each pin is melted individually and removed using suction, it is known that damage occurs at a large number of holes. This damage usually means that the periphery of the Power I (POWER I) may peel off and the bond between the internal conductive layer and the hole plating may be broken. This occurs at the temperature of the molten tin/button solder (22
The time the printed circuit board is exposed to temperatures (0°C to 250°C) combined with the heat transfer path provided by the solder in the holes;
This is because the temperature of the epoxy glass material inside the circuit board rises above its transition temperature of 120°C. Above this temperature, the rate of expansion of the printed circuit board increases rapidly such that the expansion of the epoxy glass material across the board is greater than the expansion of the conductive material. At the same time, the bonding strength between the conductive material (usually copper) and the epoxy glass material is significantly reduced.

Next, the function of the polyimide glass layer 13 will be explained. The transition temperature of polyimide glass material is from 260℃ to 280℃
It is ℃. Therefore, at a temperature of 220° C. to 250° C. of the solder wave, the loss of bonding force with the pad is minimal and the bonding of the pad to the polyimide glass layer is maintained well. As a result, the bat will not appreciably delaminate even though the pad is no longer bonded to the internal plating to which it was previously bonded. Moreover, the printed circuit board is largely made of epoxy glass, which is cheaper than polyimide glass, reducing the overall cost of the printed circuit board.

Copper-coated polyimide glass laminates are commercially available products. Therefore, the printer 1 circuit board of FIG. 1 can be made in a simple manner. The necessary epoxy glass laminates can be made using conventional procedures used in the manufacture of multilayer printed circuit boards. Similarly, a pattern of voltage planes 6 can be provided in the polyimide glass laminate. These laminates are assembled one on top of the other with the plane 6 facing inward as one outer layer to form a polyimide glass laminate.

The laminate is sandwiched between sheets of prepreg (partially cured epoxy glass) and heated to fully bond them together and fully cure.

The temperature and time required for this may be small and are more suitable for epoxy glass than the temperature and time required for polyimide glass. The possibility arises if the plane 6 is thus joined to one of the prepreg sheets, and most parts of the epoxy glass and polyimide glass do not touch each other and are therefore dependent on the bonding state of these materials. Note that it can solve certain problems. Next, an outer conductive pattern is formed and holes to be plated are drilled. next,
The printed circuit board is plated and then unplated holes are drilled and a solder resistant layer is applied.

FIG. 3 shows an example of hole placement for a pin grid array package with pins arranged in four concentric squares. Only these pins have non-plated holes 20, similar to holes 8, connected to through holes 22, similar to holes 4, either inside or outside the area 21. It should be appreciated that only a few of these holes in the solder are shown in FIG. Although it is preferable from an organizational design point of view to connect each non-plated hole to a plated through-hole by a link, it is possible to connect one non-plated hole (i.e. pin) to another, if desired.
For example, tracks may be provided straight to other components or edge connectors.

An example of suitable dimensions is a printed circuit board thickness of 0.11
4 inches (2,896 mm), polyimide material 4 x 0
．． 0.005 inches (0.127 mm), conductive layer thickness 0.005 inches (0.127 mm), conductive layer thickness 0.
0.0014 inch (0.0356 mm), and the thickness of the solder-resistant layer is 0.002 to 0.003 inch (0.0508 to 0.0762 mm). Pin is printed circuit board 9
0.040 o, oao inch (1,01,
6 to 2.032-mm).

The inventors have discovered that a composite printed circuit board of epoxy glass with an outer layer of polyimide glass, such as that described above, is capable of disassembling components even when pins are soldered to plated through holes. It has been found that there is less damage than in the case of circuit boards made entirely of epoxy glass. In some applications, especially when printed circuit boards are relatively thin, e.g.
1524 mm), the 4W components can be removed by suctioning the solder from the individual pins without causing unacceptable damage.

The anti-solder/temperature barrier increases the integrity of the circuit board to the print 1, but may be omitted if the reliability of the connections inside the hole is not important.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view through a portion of a printed circuit board;
FIG. 3 is a diagram showing some of the installed components. FIG. 2 is a top plan view of the circuit board shown in FIG. 1, with component parts omitted. FIG. 3 is a schematic diagram showing the arrangement of holes in the printed circuit board area in combination with the individual components. [Explanation of the signs of the main parts]

Claims (1)

[Claims] 1. Alternating layers of epoxy glass and conductive material, a polyimide glass layer on one side of the printed circuit board, and component connecting pins on the outer side of the polyimide glass layer. conductive pads adapted to be connected and arranged to reduce the possibility of damage to the printed circuit board during removal or replacement of installed components. Multilayer printed circuit board. 2. A multilayer printed circuit board according to claim 1, wherein a pattern of holes is provided through the layers of the printed circuit board, and these holes are arranged to receive connection pins, A multilayer printed circuit board characterized in that at least some of these holes pass through the conductive pads. 3. A multilayer printed circuit board according to claim 1 or 2, wherein a nearly complete layer of conductive material extends between a polyimide glass layer and an adjacent epoxy glass layer. A multilayer printed circuit board characterized by: 4. A method of manufacturing a multilayer printed circuit board assembly, the method comprising: a plurality of epoxy glass layers supporting conductive portions and a top layer of polyimide glass having a conductive area including conductive pads on the outer surface; are bonded together to form a stack, placing a component having connecting pins on a printed circuit board to engage at least some of the connecting pins with the conductive pads, and soldering the pins to the pads. A method characterized by: 5. The method of manufacturing a multilayer printed circuit board assembly according to claim 4, further comprising forming holes through the bonded layers to receive the connecting pins, and at least some of these holes. 1 through the conductive pad, place the component on the circuit board, the connecting pin passes through the hole, the end of the pin protrudes from the conductive pad, and the protruding end of the pin A method comprising: soldering to a pad. 6. A multilayer printed circuit board constructed as described with reference to the accompanying drawings. 7. A method of manufacturing a multilayer printed circuit board assembly as described with reference to the accompanying drawings.