JPH0152919B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for manufacturing a multilayer printed wiring board, and is a method for manufacturing a multilayer printed wiring board that facilitates countersinking of reference hole guide marks provided in advance on an inner layer wiring board. .

The main problems in lamination molding of multilayer printed wiring boards are the positioning and interlayer adhesion between the inner layer and outer layer wiring.

Interlayer adhesion is achieved by using copper foil that has been roughened or plated for adhesion to produce the inner printed wiring board, or by mechanically processing the surface of the copper foil after producing the inner printed wiring board. (surface roughening treatment - honing, etc.), chemical treatment methods (etching, oxidation treatment - coloring treatment, etc.), for example, "Multilayer printing from a patent perspective" edited by the Japan Patent Office, published by Japan Institute of Invention and Innovation, August 20, 1974 There are various methods and combinations of these (e.g., pages 185 to 189 of "Wiring Technology", Public Technical No. 78-180 of the Japan Institute of Invention and Innovation Publication Techniques), and in order to prevent the occurrence of voids, the number of prepregs used must be By controlling the molding program and once the impregnated resin in the prepreg becomes fluid, the air between the conductors is expelled by the resin, the resin is filled, and the excess resin is prevented from flowing away. This is the most common method, and in special cases - especially when it is necessary to suppress the flow of resin from the prepreg or to make the thickness of the insulating layer thinner compared to the thickness of the inner layer copper foil, the method of interlayer insulating resin layer In cases where it is necessary to control thickness accuracy extremely strictly,
There is a method in which a wiring copper foil and an insulating resin substrate surface are made flat in advance as an inner layer wiring board.

Furthermore, a method for aligning inner layer wiring and outer layer wiring is described on pages 194 to 196 of ``Multilayer Printed Wiring Technology from a Patent Perspective'' cited above. A method of forming a multilayer board by inserting pins into the reference holes, etc. of multiple sets of multilayer materials forming a wiring network having reference holes, etc. for positioning during molding, and performing multilayer molding once. After forming a multi-layer structure by stacking outer layer prepreg and copper foil or prepreg and single-sided copper clad laminate on an inner layer wiring board on which reference hole guide marks have been provided in advance, the reference hole guide marks are counter-sunk and the reference holes are formed. There are two common methods: drilling a hole and forming a circuit on the outer layer based on the reference hole.

In the case of the above method, after multi-layer molding, the reference hole guide mark is hidden by the laminated outer layer, so in order to make the reference hole, "spot boring" is performed to expose the reference hole guide mark and then drill the reference hole. Is required. However, the reference hole guide mark part is usually hidden by the laminated outer layer, so in order to counterbore, it is necessary to apply a film of the inner layer pattern to determine the approximate position, or to correct any ``embossed'' part of the inner layer pattern. I looked at it, decided on a position, and then proceeded to counterbore. However, this method has drawbacks such as difficulty in positioning the counterbore and long working time.Especially in the case of a layer structure in which the distance between the outer layer and the middle layer (inner layer) is large, the inner layer pattern hardly becomes embossed. The shortcomings were noticeable.

As an improvement method that does not require counterboring, a reference hole is provided in the reference hole guide mark part previously formed on the inner layer wiring board, and this reference hole becomes the outside (=surrounding) of the outer layer laminate material and is covered with the outer layer material. There is a method of stacking the outer layer material and forming a multi-layer molding so that the inner layer material does not overlap, but in this method, it is essential to design the reference hole guide mark part of the inner layer material and the inner layer printed wiring part to be separated in advance, and furthermore, There are problems such as differences in dimensional change behavior due to differences in heat and pressure loads between the reference hole guide mark portion and the portion covered by the outer layer material, which limits the applicable multilayer plates.

The present invention has been completed as a result of intensive study on a method for more easily counterboring reference hole guide marks in the above method, and by discovering a method for overcoming the above drawbacks.

That is, in the present invention, prepreg and copper foil for the outer layer are stacked and formed into a multilayered structure on an inner layer wiring board provided with a reference hole guide mark, and then a reference hole is formed in the guide mark, and the outer layer is formed based on the reference hole. In a method for manufacturing a multilayer printed wiring board that forms a circuit, an inner layer wiring board with a hole smaller than the reference hole diameter in the center of the guide mark is used as an inner layer wiring board to form a multilayer printed wiring board, and the This method of manufacturing a multilayer printed wiring board is characterized in that a recessed portion formed in a guide mark portion is counterbored, a reference hole is made, and then wiring in an outer layer is formed based on the reference hole.

In the present invention, when using an inner layer wiring board with a hole smaller than the reference hole diameter in the center of the reference hole guide mark, since the hole is hollow, resin flows from the upper and lower prepregs and is heated and cured as it is. . At this time, if the volume of the hole is at least the same as the amount of resin flowing in from the upper and lower prepregs, or if the amount of resin is significantly larger than the amount of resin sufficient to fill the gap between the printed wiring copper foils, the hole should be filled with air. Either the hole is cured as it is, or the hole is filled with resin, but the hole is cured under extremely low pressure compared to other parts. As a result, the lamination molding pressure was significantly different between the reference hole guide mark part formed around the hole and the hole, and for the same reason as emphasizing the "embossedness" of the inner layer pattern, the reference hole guide mark was This will be easily recognized visually as an embossment and a depression in the hole.

The reason for this is presumed to be as follows.

In conventional multilayer lamination molding, the inner layer wiring pattern ``emerges'' when the distance between the inner layer pattern and the outer layer is small, that is, when the thickness and number of prepregs stacked in the middle are relatively small, as described above. It becomes noticeable. In addition, copper clad laminates,
On the surface of a copper foil such as a multilayer board, the weave of the glass woven fabric (usually a plain woven fabric) used for the prepreg can be clearly recognized.

First, the resin impregnated into the prepreg becomes fluid due to heating in the early stage of lamination molding, flows into the spaces between the wiring copper foils of the inner layer wiring board, fills the gaps, gels, and then completely hardens. Once gelled, it does not flow at all even under pressure during lamination molding.

Until the resin gels, the resin in the prepreg on the wiring network of the inner layer wiring board flows out and fills the gaps between the conductors, and the pressing pressure in this process is mainly applied to the prepreg on the wiring network and The load will be applied to the copper foil. In addition, during the process of gelling and curing, the resin undergoes curing shrinkage, and as a result, the gelled resin in the prepreg on the wiring network of the inner layer wiring board is smaller than the resin in the prepreg between the conductors. Since the amount of curing shrinkage is small, the press pressure is also applied mainly to the prepreg and copper foil on the wiring network.

As a result, a greater pressure than the average pressing pressure is applied to the part of the outer layer copper foil of the multilayer board that is above the wiring network of the inner layer wiring board, and a smaller pressure is applied between the wiring networks. Due to the difference, the surface condition of the copper foil is different between the portion of the inner layer wiring board above the wiring network and the area between the wiring networks.
Further, because of the above, the outer layer copper foil on the wiring network portion of the inner layer wiring board has a concave dent compared to the outer layer copper foil on the wiring network portion of the inner layer wiring board.

Therefore, it is presumed that the difference in the surface condition of the copper foil and the slight difference in the degree of unevenness will be recognized as the "embossment" of the inner layer wiring pattern. However, the reason why the lifting becomes more noticeable is because there is less prepreg, so the amount of resin that flows out from the prepreg increases, and the difference between the top of the wiring conductor and the area between them becomes large, and therefore the difference in pressing pressure becomes relatively large. , and the press pressure applied to the copper foil on the wiring conductor of the inner layer wiring board is more direct, so the boundary between the inner layer wiring pattern part and the space between them becomes clearer, and the dent between the inner layer wiring pattern part and the space between them becomes slightly larger. It is presumed that this is based on the following.

If the above is true, the top of the inner layer wiring should be raised, and the area between should be a depression, and although it may seem possible to quantify this by measurement, etc., this can be quantified by measuring the sum of the unevenness. That has not been successful. The reason for this is that in addition to the embossment of the inner layer wiring pattern described above, the surface of the outer copper foil has irregularities (3 to 4 μm degree, clearly visible to the naked eye),
Furthermore, even if there is a difference in the degree of unevenness due to the above-mentioned reasons, when a similar calculation is made to calculate the amount of depression in the hole described later, the unevenness is at most 1 μm or less, and the change is extremely smooth. As a result, it is thought that it cannot be quantified by measurement using an unevenness meter.

Next, the reason why the reference hole guide mark portion of the present invention is extremely easily recognized as an embossed or recessed portion is similar to the above case, and is presumed to be a result of this being emphasized.

In other words, the hole formed in the reference hole guide mark part has an extremely large difference (usually 70 μm or less for the former and 1600-70 = 1530 μm for the latter) compared to the difference between the wiring conductor on the inner layer wiring board and the gap between them. be. As a result, the pressing pressure required to gel the outer layer copper foil around the hole formed in the reference hole guide mark is extremely different from that of the outer layer copper foil above the hole. Also,
Differences in curing shrinkage and thermal expansion coefficient after gelation also result in large differences. Here, the curing shrinkage (linear shrinkage rate) of the resin is 0.6%, the specific gravity is 1.2, and the specific gravity of the glass cloth base material.
2.5, Thermal expansion coefficient (linear expansion coefficient) of resin and glass cloth base material
Assuming that the difference in is △=50×10 ^-6 cm/cm/℃, and assuming that the hole is also completely filled with resin,
For a 1.6mm thick shield plate, assuming no volume effect, the difference due to curing shrinkage is 0.0064mm. ●Around the hole; (1.6−0.74−0.07)×(40/1.2)/(60/2.5
+40/1.2)×(0.6/100)=0.00275 ●Hole part; (1.6−0.07)×(0.6/100)=0.00918 Difference due to difference in thermal expansion coefficient; 0.0052mm. ●Around the hole; (1.6−0.21)×(40/1.2)/60/2.5+40/1.2)×
△×(170−25)=117△ ●Hole part; (1.6−0.07)×△×(170−25)=221.8△ ∴(221.8−117)×△=5.24×10 ^-3 mm From the above, hole The copper foil on the part is smaller than the area around the hole.
This results in a depression of 5.8 μm.

Therefore, in the case of the present invention, the copper foil above the hole portion is hardly subjected to press pressure, whereas the area around the hole is subjected to press pressure.
As a result, the surface condition of the copper foil is greatly different between the area above the hole and the area around it. Furthermore, as is clear from the calculations above, the hole is depressed by approximately 6 μm, and the normal inner layer wiring pattern is exposed. It is estimated that there will be a huge difference compared to the above, and that it will be easily observable visually.

As described above, the reference hole guide mark portion formed on the inner layer has a concave inner surface and is raised, and can be easily identified visually. Therefore, the location for spot boring can be determined at a glance, which has the advantage of eliminating work errors and shortening the work time.

The present invention will be described below with reference to Examples.

Example 1 Board thickness 0.6mm (70μm double-sided copper clad board, copper foil combined)
A desired wiring network was created on the inner layer material (0.74 mm) by a photoprinting-etching process. At this time, the hole diameter of the guide marks made at the four corners was 4.0 mmφ.

After drilling a 2.8 mm diameter hole in the center of this guide mark, the copper foil wiring created was treated with a black oxide coating, which is a type of surface treatment for adhesives (an aqueous solution containing sodium hypozinc oxide and sodium hydroxide as main components). in
After that, 5 sheets each of 0.1 mm thick glass woven epoxy resin-impregnated prepreg (resin amount 40 wt%) and 1 sheet each of 35 μm thick copper foil were applied on both sides. The material was placed at 160°C to 170°C and pressed at a temperature and pressure of 40Kg/cm ² for 60 minutes. (In the above, the volume of the hole is larger than the resin amount of the upper and lower prepregs with the same diameter as the hole.) Take out a 1.6 mm thick double-sided untreated copper foil multilayer board (shield board) from the press, When I observed it,
Although the embossment of the wiring pattern on the inner layer wiring board was extremely small, the guide marks provided at the four corners were clearly distinguishable as dents.

Determine the counterbore position using this indentation, counterbore (expose) the guide mark on the inner layer wiring board with a counterbore drill, and then use a drill machine with a projector to place the 3.175mm in the center of the guide mark based on the counterbore guide mark.
A hole of mmφ was drilled.

The time required for the above counterbore positioning, counterbore, and hole drilling processing was 3 minutes/piece (4 places/piece),
It was less than half of Comparative Example 1.

Using these holes, an outer layer wiring network was formed by photoprinting and etching to obtain a multilayer printed wiring board.

Comparative Example 1 A multilayer shield board was manufactured in the same manner as in Example 1, except that a hole was not made in the center of the guide mark of the inner layer wiring board.

On the surface of the outer layer of this multilayer shield plate taken out from the press, there was a very small embossment of the wiring pattern of the inner layer wiring board, and it was possible to roughly identify it.

Determine the approximate counterbore position by embossing this wiring pattern, counterbore (expose) the guide mark on the inner layer wiring board with a counterbore drill, and place the projector in the center based on the counterbore guide mark. I drilled a 3.175mmφ hole with a drill machine.

The time required for the above-mentioned counterbore positioning, counterbore, and hole-drilling processing was 8 minutes/sheet (4 locations/sheet).

Claims (1)

[Claims] 1. On the inner layer wiring board with reference hole guide marks,
In the method for manufacturing an outer layer printed wiring board, in which prepreg and copper foil for the outer layer are stacked and multi-layer molded, reference holes are formed in the guide marks, and a wiring network for the outer layer is formed based on the reference holes. A recessed portion formed in the guide mark portion of a multilayer board obtained by multilayer molding using an inner layer wiring board with a hole smaller than the reference hole diameter in the center of the guide mark, or a recessed portion of the guide mark. A method for manufacturing a multilayer printed wiring board, which comprises countersinking a raised portion, drilling a reference hole, and then forming wiring in an outer layer based on the reference hole.