JPS6318646A - Element part for printed board - Google Patents

Abstract

PURPOSE:To decrease the generation of the swelling of plating at the bottom surface, by performing spot facing of the bottom surface on the recess part at the central part of the upper surface of a substrate, thereby increasing mechanical adhesive strength. CONSTITUTION:A glass fiber reinforced plastic substrate 1 is constituted by alternately laminating an epoxy resin layer 6 and glass textile layers 6 comprising the woven fabric of glass fiber. A square recess part 2 undergoes spot facing from the upper surface of the substrate 1 so that a bottom surface 3 approximately agrees with the central line of the textile layers 5. Copper is plated 4 on the surface. Nickel and gold are plated on the copper plating 4 by an electrolysis method, and corrosion resistance is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an element part for a printed circuit board, and particularly to an element part whose base material is glass fiber reinforced plastic.

"Conventional Technology" Conventionally, alumina PGA made from alumina was the mainstream for printed circuit board element parts (hereinafter referred to as PGA) used as packages for ICs, LSIs, etc., but recently plastics made from glass 1filt reinforced plastic have been used. PG△ is now being widely used. This reduces the cost of plastic PGA by 1/3 to 1/4 compared to alumina PGA, and also reduces mechanical impact and g1
m circuit formation, circuit pattern accuracy, external dimension accuracy,
This is because the package design can be changed easily.

Conventional plastic PGAs have a recess in the center of the upper surface of a glass fiber-reinforced plastic substrate, the entire bottom and side surfaces of which are plated with gold, and a large number of microcircuits that are plated with gold around the recess so as not to come into contact with the gold plating of the recess. and,
The board is passed through 1:1 and one end is connected to each of the microcircuits, and the other end has a large number of lead pins protruding from the bottom surface of the board, and an element such as an IC or an SI is mounted in the recessed part to form the element. Each of the lead wires is connected to the inner end of each microcircuit.

This plastic PGA glass taII! Generally, glass-epoxy laminates, glass-high heat-resistant epoxy resin laminates, glass-bismaleimide triazine laminates, etc. can be used for the reinforced plastic substrate, but the temperature is 150°C to 180°C during the process of attaching elements later. Glass-high heat resistant epoxy laminates are most commonly used to withstand high temperatures. The thickness of the substrate is often 1.0 to 2.0 m, and a thickness of 1.6 threshold is most often used. The recess for mounting the element is formed by counterbore the surface of the board, and its depth depends on the shape of the element to be mounted and the PGA.
Although it varies depending on the structure etc., generally 0.30m"-0,
Within a range of 70m, the most common depth is 0.50Ill
1m±0.10INA. If this recess n1 is left counterbored, trace amounts of moisture and impurities contained in the substrate will leach out from the bottom and surrounding areas of the recess and have a harmful effect on the elements mounted on the tower, so the entire surface of the four parts is plated. It is coated to block the influence of trace amounts of moisture.

The plating of this recess was first done by electroless copper plating with 0.2
An extremely thin ground layer of approximately μm thickness is formed, and 20
Electrolytic copper plating is applied to a thickness of about .mu.m, and finally, in order to provide sufficient corrosion resistance, nickel plating of about 5 .mu.m and gold plating of about 0.5 .mu.m is applied electrolytically on the electrolytic copper plating.

"Problems to be Solved by the Invention" The conventional plastic PGA mentioned above has a defect in that the plating layer applied to the four parts bulges up from the bottom of the recess due to peeling of the bottom layer electroless copper plating. . In addition, when such blistering of the plating layer occurs, unevenness occurs on the bottom surface, which not only makes it impossible to stably mount the device in the recess, but also prevents post-processing, such as the step of bonding the device to the bottom surface with resin.
Temperatures of 150℃ to 180℃ are used in the wire bonding process, the process of sealing elements with resin, etc. The problem is that the plating peels off from the swollen parts because it is exposed to 3 degrees of temperature. Furthermore, if the plating peels off from the bottom of the recess,
Troubles such as incomplete fixation of the element and breakage of gold wires connected by wire bonding and moisture infiltration from the bottom surface occur.

[Means for Solving the Problems] In order to solve the above-mentioned problems of the conventional plastic PGA, the present invention provides that when a recess to be plated is counterbored on the surface of a glass fiber reinforced plastic substrate, the bottom surface of the recess is It is characterized in that it is processed so that it is located on the glass cloth layer in the substrate.

"Function" The bottom layer of electroless copper plating in J3 on the plating layer applied to the recess of the plastic PGA is bonded by the mechanical hooking effect (anchor effect) of chemically deposited metal crystals to the bottom of the recess. Therefore, if the bottom of the concave part is a smooth plastic snack, the adhesive strength is weak and it is easy to peel off, but in the present invention, the bottom of the four parts is counterboreed so that it is located on the glass cloth layer, so the bottom is rough due to the exposed glass cloth. Since the mechanical adhesion is strengthened, the occurrence of blistering of the plating on the bottom can be greatly reduced.

"Example" FIG. 1 is a cross-sectional view showing the outline of the main parts of the plastic PGA according to the present invention, in which the glass IJ & fiber-reinforced plastic substrate 1 has an epoxy resin layer 6 and a glass cloth layer 5 made of glass tag fabric alternately. A rectangular recess 2 is counterbored from the top surface of the substrate 1 so that its bottom surface 3 substantially coincides with the center line of the glass cloth layer 5, and copper plating 4 is applied thereon. The copper plating 4 is obtained by first depositing a chemical copper layer with a thickness of about 0.2 μm by electroless copper plating, and then applying electrolytic copper plating with a thickness of about 20 μm using this as a base. Although not shown, nickel plating and gold plating are usually applied on the copper plating 4 by an electrolytic method in order to provide corrosion resistance.

Figure 2 is a plan view of the bottom of the recess shown in Figure 1 before plating, and shows that the knots of the warp and weft of the glass cloth form a cross-shaped pattern and stand out on the bottom, forming a river surface. . Fig. 3 shows an enlarged view of the state of the plating layer near the bottom of the recess shown in Fig. 1. Chemical copper Fm4a is deposited on the bottom surface, which is roughened by the glass cloth layer 5 exposed by counterbore processing, and It can be seen that the electrolytic copper layer 4b is plated on. Since the chemical copper layer 4a is coated on a rough surface having irregularities, it is difficult to peel off due to the anchor effect.

FIG. 4 shows a case where the bottom surface 3' of the recess 2' is located in a layer 6 made of only epoxy resin between the glass cloth layers 5, and 7 is a polygonal filler for the space created by the swelling of the copper plating layer 4 on the bottom surface 3'.

In this case, a completely smooth layer of epoxy resin appears on the bottom surface 3' as shown in FIG. FIG. 6 shows an enlarged view of the state of the plating layer near the bottom of the recess in FIG. 4. Since the chemical copper layer 4a is deposited on the smooth surface of the epoxy resin 6, the thermal Or, it is easy to cause peeling due to mechanical impact and create a space 7.

Therefore, the present invention counterbores the bottom surface 3 of the recess 2 so that it is located on the glass cloth layer 5 as shown in FIG. However, the rate of occurrence of blisters varies greatly depending on the position of the bottom surface 3 with respect to the glass cloth layer 5. That is, the proportion of glass fibers forming the rough surface on the bottom surface 3 is maximum when the bottom surface is located at the center of the glass cloth layer, decreases as the bottom surface deviates vertically from there, and reaches O when the bottom surface 3 completely deviates from the glass cloth layer. This is because the anchor effect changes accordingly. According to the experimental results, when the original thickness of the glass cloth used as a reinforcing material for the substrate is 0.1 m, the bottom of the recess is within ±0.03 mm from the center line of the glass cloth layer. The incidence of blistering was 0, and the rate of blistering increased rapidly as the glass cloth layer was removed from the range, and the rate of blistering was 50% or more when the glass cloth layer was completely removed.

Further, when the original thickness of the glass cloth was 0.2M, the occurrence rate of blistering was ○ when the position of the bottom of the recess was within the range of ±0.06 mm from the center line of the glass cloth layer.

Therefore, if the counterbore is processed so that the bottom of the recess is within ±30% of the original thickness of the glass 15 used from the center line of the glass cloth layer, the occurrence of blistering in the copper plating layer can be almost suppressed. can. The type of glass cloth used for the substrate, the number of laminated sheets, and the position occupied by the glass cloth layer in the thickness direction of the substrate are almost constant depending on the type of substrate.
Since the condition can be known by inspecting the cut cross section of the substrate, the position of the bottom surface of the recess to be automatically counterbored can be set in advance based on the inspection result.

Experimental Example 1 Glass epoxy double-sided printed wiring board using glass cloth with a thickness of 0.1 mm as a reinforcing material (in order of thickness 1.6,
When we measured the position of the glass cloth layer by cutting a cross section of a laminated cloth (10 sheets), we found that the center line of the fourth glass cloth layer from the top of the board was approximately 0.56 m from the top of the board. The thickness was approximately ±0.07 rnm with respect to the center line. Additionally, above and below the glass cloth layer was a layer of epoxy resin only, approximately 0.02 m thick. 50 rectangular recesses of a constant depth are counterbored on one substrate with the above structure, and 50 rectangular recesses of a constant depth are counterbored with different depths on another substrate with the same structure. In this way, several substrates were prepared in which 50 rectangular concave portions were counterbored at different depths for each substrate. The position of the bottom surface of the concave portion of each substrate is above the center line of the fourth glass cloth layer (depth of 0.56 m from the top surface of the substrate), ±0.03 M, ±0.04 am from the same center line,
±0.06mm, ±0.08m1. : Set. Electroless copper plating and electrolytic copper plating were applied to each board with the above-mentioned recesses counter-bored, and the occurrence of blistering in the copper plating on the bottom of the back end after the specified process was inspected. The results are shown in Table 1. I got it.

The blistering rate was determined visually using a 10x magnifying glass. Even if there was one blister in the copper plating layer on the bottom of the recess, it was considered that there was a blister, and the occurrence rate was determined from the number of recesses that were considered to have blisters among the 50 four parts.

Experimental Example 2 Cross section of a glass epoxy printed wiring board (board thickness 0.4M) constructed by laminating one glass cloth with a thickness of 0.2rMR between two sheets of glass cloth with a thickness of 0.1M as a reinforcing material. When I measured the position of the glass cloth layer,
The center line of the second 0.2 mm thick glass cloth layer from the top surface of the substrate was located 0.2 m from the top surface of the substrate, and the layer thickness was approximately ±0.1# with respect to the center line. Counterbore 50 rectangular parts of a certain depth on one board with the above structure,
Furthermore, 50 rectangular recesses of a constant depth were counterbored on another board with the same structure, and in this way, the depth was changed for each board and 50 rectangular recesses were counterbored. A number of boards were prepared. The position of the bottom of the concave portion of each board is above the center line of the second glass cloth layer (0.2 m depth from the top of the board), ±0.03 am, ±0.06 mm from the same center line,
It was set at ±0.07m and ±0.09m. Electroless copper plating and electrolytic copper plating were applied to each board with the above-mentioned recesses counterbore processed, and after passing through the prescribed process, the occurrence of blistering of the copper plating on the bottom of the recesses was inspected, and the results are shown in Table 2. Obtained.

``Effects of the Invention'' The present invention is characterized in that when counterboring the recesses formed on the upper surface of the substrate in a plastic PGA, the bottom surface is positioned on the glass cloth layer in the substrate as described above, so that the plating is applied to the bottom surface of the four parts. It was possible to increase the anchoring effect of the layer and significantly reduce the occurrence of blistering in the plating layer. In particular, when the bottom surface of the recess is located within the range of ±30% of the original thickness of the glass cloth layer from the center line of the glass cloth layer, the occurrence of blisters can be almost completely eliminated.

[Brief explanation of drawings]

FIG. 1 is a sectional view schematically showing the main parts of a plastic PGA according to the present invention. FIG. 2 is a plan view without showing the pattern of the bottom surface of the recess before plating of the plastic PGA according to the present invention. FIG. 3 is an enlarged cross-sectional view showing the state of the plating layer near the bottom of the recess shown in FIG. Figure 4 shows the R of the main part of a conventional general plastic PGA.
It is a sectional view showing the main points. FIG. 5 is a plan view showing the pattern of the bottom surface of the recess before plating of the plastic PGA shown in FIG. 4. FIG. 6 is an enlarged cross-sectional view showing the state of the plating layer near the bottom of the recess shown in FIG. 4. FIG. DESCRIPTION OF SYMBOLS 1... Glass fiber reinforced plastic board, 2... Recessed part, 3... Bottom surface, 4... Copper plating layer, 5... Glass cloth layer, 6... Epoxy resin layer.

Claims (2)

[Claims] (1) In a printed circuit board element component having a recessed portion to be plated in the center of the upper surface of a glass fiber-reinforced plastic substrate, the recessed portion is counterbored so that its bottom surface is located on the glass cloth layer in the plastic substrate. Element parts for printed circuit boards characterized by: (2) The printed circuit board according to claim (1), wherein the bottom surface of the recess is within a range of ±30% of the original thickness of the glass cloth layer from the center line of the glass cloth layer. Element parts.