JPH022315B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mounting structure for a lead wireless semiconductor device.

A leadless semiconductor device refers to a semiconductor case made of ceramic or the like that does not have a metal lead electrode but has an electrode such as a solder, such as a chip carrier, a leadless inverted device, or a silicon element.

An example of the mounting structure of a conventional lead wireless semiconductor device is shown in FIGS. 1 and 2.

FIGS. 1a and 1b show a silicon element 1 connected to an alumina substrate 2 by a brazing material 3 such as solder, and this connection method is called flip-chip bonding.

Figure 2 a and b show alumina chip carrier 4.
is connected to a printed wiring board 5 made of a glass cloth base material impregnated with epoxy resin by a brazing material 6 such as solder.

In a structure in which a silicon element 1 or a chip carrier 4 is connected to an alumina substrate 2 or a printed wiring board 5 by brazing fillers 3 and 6 as shown in FIGS. 1 and 2, repeated temperature changes may cause the brazing fillers 3 and 6 to will fail due to fatigue.

This will be explained with reference to FIG. 3, taking as an example the chip carrier 4 shown in FIGS. 2a and 2b.

FIG. 3 is an enlarged view of the brazing material 6 of the chip carrier 4 shown in FIG.
A chip carrier 4 made of alumina material is connected by a brazing material 6 to a conductor 7 on a printed wiring board 5 made of a glass cloth substrate impregnated with epoxy resin.

In this structure, when a temperature change ΔT is added,
There is a difference between the elongation of the printed wiring board 5 and the elongation of the chip carrier 4, and the brazing filler metal 6 shifts between the printed wiring board 5 side and the chip carrier 4 side △l △l=l・△α・△T/2 ...(1 ) occurs. In equation (1), Δα is the difference in linear expansion coefficient between the printed wiring board 5 and the chip carrier 4, and l is the size of the chip carrier 4.

This deviation Δl causes approximate shear strain γ γ=Δl/h (2) in the brazing filler metal 6. In equation (2), h is the thickness of the brazing filler metal 6.

When temperature changes are repeated (hereinafter referred to as temperature cycles), shear strain γ is repeatedly generated in the brazing filler metal 6, causing fatigue failure of the brazing filler metal 6. The number of repetitions of temperature changes (hereinafter referred to as temperature cycle life) of the brazing filler metal 6 until fatigue failure occurs is expressed as N=C/γ ² (3). Substituting equations (1) and (2) into equation (3), it is expressed as N=C(2h/l・△α・△T) ² ...(4). In equation (4), C is a constant determined by the material of the solder.

From equation (4), it can be seen that the temperature cycle life is long when the difference in linear expansion coefficient between the chip carrier 4 and the printed wiring board 5 is small, and short when the difference is large.

The linear expansion coefficients of silicone, alumina, and glass cloth base epoxy resin are 3×10 ^-6 ℃ ^-1 and 6~, respectively.
Because there is a large difference between 8×10 ^-6 ℃ and 13 to 20×10 ^-6 ℃,
Connecting the silicon element 1 to the alumina substrate 2,
When alumina chip carriers 4 are connected to a glass cloth substrate epoxy resin impregnated printed wiring board 5, the temperature cycling life of these connections is considerably limited.

Recently, aromatic polyamide fiber cloth with a negative coefficient of linear expansion, such as Kevlar fiber cloth (registered trademark of DuPont), has been used as a lamination cloth for substrates on which semiconductor devices without lead wires can be mounted. ing. Using this cross,
When manufacturing a substrate, the coefficient of linear expansion of the substrate is determined by the fiber content of the cloth.

Figure 4 shows the function of the volume content of Kevlar fibers and the coefficient of linear expansion of the substrate when the substrate is manufactured using Kevlar fiber cloth as the aromatic polyamide fiber and epoxy resin as the thermosetting resin. It is something.

However, the above-mentioned aromatic polyamide fiber cloth is extremely expensive compared to glass cloth, and glass cloth is less compatible with the resins used as matrices, such as epoxy resin, silicone resin, and unsaturated polyester resin. Since it is inferior in comparison, there is a problem in that peeling tends to occur in the laminate at the cross border.

On the other hand, semiconductor devices generate heat during operation. In order for semiconductor devices to operate accurately, this heat must be dissipated.
It is necessary to prevent overheating of semiconductor devices. Heat generated in a semiconductor device is dissipated by being released from the surface of the semiconductor device or conducted to the substrate.

Therefore, it is desirable that the substrate on which the semiconductor device is mounted has high thermal conductivity.

However, aromatic polyamide fibers have a relatively low thermal conductivity, so the thermal conductivity of a substrate made of these fibers and a thermosetting resin is lower than that of a glass cloth-based epoxy resin substrate or an alumina substrate. Semiconductor devices mounted on substrates made of aromatic polyamide fibers and thermosetting resins have the disadvantage of being easily overheated.

Furthermore, if the fiber content in the laminate is too high or too low, the arrangement of the fibers in the resin tends to be disordered, resulting in locally uneven fiber content in the laminate. There is. A laminate having such non-uniform portions has different dimensions over time in different parts of the laminate, resulting in misalignment of the wiring in the laminate. This phenomenon is called registration.

Therefore, when this registration occurs,
Multilayer wiring boards (laminated boards with conductor wiring on the surface (first prepreg, usually a set of a predetermined number of prepreg layers) are stacked together, and at that time,
Prepreg between each laminate (second prepreg)
A printed wiring board that is pressurized and heated by sandwiching it. usually,
The first prepreg and the second prepreg are made of the same material. ) and double-sided copper-clad boards (printed wiring boards with copper wiring on both the upper and lower surfaces of a plurality of prepreg laminates), the conductor wiring in each layer moves horizontally, causing misalignment in the vertical direction. In addition, in a printed wiring board in which conductor wiring is provided only on one side (single layer), wiring deviation in the horizontal direction occurs due to registration. Especially wiring (continuity)
Defects are an important problem in multilayer wiring boards and double-sided copper-clad boards that cause vertical misalignment.

However, when creating a wiring board with a desired coefficient of linear expansion using a laminate made of the above-mentioned Kevlar fiber cloth, aromatic polyamide fiber fibers in the laminate or prepreg are used to achieve the desired coefficient of linear expansion. Since the fiber content is determined as shown in FIG. 4, registration may easily occur at this fiber content when producing a substrate.

As a result of intensive studies to solve the above-mentioned problems of the conventional technology, the present inventors found that a composite cloth made by combining aromatic polyamide fibers and glass fibers has good affinity with the resin used as a matrix. The present inventors have discovered that it is possible to provide a mounting structure in which peeling does not easily occur in a laminated board at cross boundaries, has good thermal conductivity, and is difficult to cause registration, and has thus arrived at the present invention.

The present invention has been made based on the above-mentioned points, and has good affinity with the resin used as a matrix, is difficult to peel off at the interface of the cloth in a laminate, has good thermal conductivity, and has good compatibility with the resin used as a matrix. It is an object of the present invention to provide a lead wire-less semiconductor device that can have a long temperature cycle life in which shock is less likely to occur.

The present invention is characterized by using as a base material a composite cloth made of a composite yarn made of mixed twisted aromatic polyamide fibers and glass fibers,
A prepreg is formed by impregnating this composite cloth with a thermosetting resin. A multilayer wiring board is formed by stacking multiple sheets of prepreg, wiring metal foil as a conductor on its surface to form an intermediate laminate, and then laminating these intermediate laminates with the same prepreg and molding them under heat and pressure. do. Alternatively, a predetermined number of sheets of this prepreg are laminated, metal foil is conductor wired on both sides of the prepreg, and the same is heated and pressurized to form a double-sided wiring board. In short, a plurality of prepregs and a plurality of metal wiring layers are heated and pressure-molded to form a printed wiring board. The linear expansion coefficients of these printed wiring boards are matched to the linear expansion coefficients of the lead wireless semiconductor devices, and the lead wireless semiconductor devices are mounted on these printed wiring boards.

Hereinafter, one embodiment of the mounting structure of the lead wireless semiconductor device of the present invention will be described with reference to FIG.

FIGS. 5a and 5b show the case of a multilayer wiring board as an example of the mounting structure of the lead wireless semiconductor device of the present invention.

Prepreg is created by impregnating a thermosetting resin into a plain-woven cloth made from composite yarns made by twisting Kevlar 49 fiber, a type of aromatic polyamide fiber, and glass fiber, and then laminating a predetermined number of sheets to create a prepreg. A copper clad laminate 8 is obtained by overlapping copper foil and heating and press-forming.

This copper-clad laminate 8 is photo-etched to form copper wiring 9 on its surface, and then several copper-clad laminates 8 and the prepreg are stacked on top of each other and pressed.
Printed wiring boards are made by heating, drilling holes, plating through holes, and photo-etching copper wiring on the outer layer.

As described above, an alumina chip carrier 11 containing a computer LSI is connected by solder 12 to the copper-clad laminate 8, ie, the printed wiring board, which has the copper wiring 9 inside and has the through holes 10.

FIGS. 6a and 6b show another example of the mounting structure of the lead wireless semiconductor device of the present invention, which is an example of a structure in which a silicon element, which is a control IC for an automobile, is mounted.

Laminated board 1 with through holes 13 and copper wiring 14
5, a silicon element 16 is connected to the substrate by solder 17. This laminate 15 is made in the same manner as the multilayer printed wiring board shown in FIG. The coefficient of linear expansion of the laminate 15 is matched to that of the silicon element 16, and since there are large temperature changes inside an automobile, the coefficient of linear expansion of the laminate 15 is matched to that of the silicon element 16.
It is important to maintain the reliability of the connection of the silicon element 16 that they have the same coefficient of linear expansion.

In the above-described embodiment, a composite cloth made by twisting aromatic polyamide fibers and glass fibers is plain-woven.

The above-mentioned laminate can have an arbitrary coefficient of linear expansion within a certain range by changing the content of the composite cloth and thermosetting resin. The relationship between the change in the content of the composite cloth and thermosetting resin and the linear expansion coefficient of the laminate is as follows.

The relationship between the coefficient of linear expansion of the laminate and the fiber volume content (the proportion of the composite cloth in the laminate; therefore, the volume of the thermosetting resin is subtracted from the total volume of the laminate) is approximately expressed by the following equation (1 ).

α _isp = 1/2 [(α ₁₁ + α ₂₂ ) + (E ₁₁ − E ₂₂ )・(α ₁₁ − α ₂₂ )/E ₁₁ + (1+2ν
₁₂ )・E ₂₂ ](1) α _isp is the linear expansion coefficient of the laminate, and each symbol in equation (1) is represented by the following equations (2) to (7).

α ₁₁ =V _f・E _f・α _f +V _n・E _n・α _n /V _f・E _f +V _n・E _n (2
) α ₂₂ = (1+ν _f )・V _f・α _f + (1+ν _n )・V _n・α _n −α ₁₁・ν ₁₂ (3) ν ₁₂ = V _f・ν _f +V _n・ν _n (4) E ₁₁ =V _f・E _f +V _n・E _n (5) E ₂₂ =1+2V _f・η/1−V _f・η・E _n (6) η=Ef/Em−1/Ef/Em+2 (7) Here, f is fiber, m is resin, 11 is fiber direction,
22 means the direction perpendicular to the fibers, V means the volume content, E means Young's modulus, α means the coefficient of linear expansion, and ν means Poisson's ratio.

Also, based on the above equations, the linear expansion coefficient and Young's modulus of composite fibers made of mixed twisted yarn can be approximately calculated using the following equations (8) and (9).
It is expressed as

α _f ＝V _k・E _k・α _k ＋V _G・E _G・α _G ／V _k・E _k ＋V _G・E _G (8) E _f ＝V _k・E _k ＋V _G・E _G (9) Here K indicates aromatic polyamide fiber and G indicates glass fiber.

Figure 7 shows the number 22.5 tex (1 tex is 10 ^-6
Kg/m) of glass fiber and aromatic polyamide fiber of 22.5 tex (specifically, poly-P-
Expressions (1) to (9) express the relationship between the volume content of fibers and the coefficient of linear expansion of the laminate of a laminate made of epoxy resin and a composite cloth prepared by plain weaving mixed yarns of two phenylene terephthalamide fibers. ) and the measured results (circles in the figure), and it can be seen that they almost match. By selecting the content of the composite cloth (or thermosetting resin) according to this figure, it is possible to determine the linear expansion coefficient of the laminate.

In addition, laminates using this composite cloth have higher thermal conductivity than laminates made of cloth made only of aromatic polyamide fibers, and the fiber content in the laminate remains at a value that does not easily cause registration. Then, we determined the appropriate composite ratio of aromatic polyamide fiber and glass fiber in the composite cloth.
A laminate having a desired coefficient of linear expansion can be created. The relationship between the composite ratio of aromatic polyamide fiber and glass fiber and the linear expansion coefficient of the laminate is as follows.

First, using the above formulas (1) to (9), as an example, when the volume content of the composite fiber is 44.8%, the volume content of poly-P-phenylene terephthalamide fiber (poly-P with respect to the total volume of the fiber) The relationship between the volume ratio of phenylene terephthalamide fibers and the coefficient of linear expansion of the laminate is calculated and shown as a solid line in Figure 8. The circle mark in the diagram is one glass fiber with a count of 22.5 tex and the count
This is an actual value when the volume content of poly-P-phenylene terephthalamide fiber is 77.6% using a composite cloth made by plain weaving two mixed twisted yarns of poly-P-phenylene terephthalamide fiber of 22.5 tex.

Therefore, by selecting the aromatic polyamide fiber content according to FIG. 8, the linear expansion coefficient of the laminate can be determined.

Furthermore, the relationship between the content rate of thermosetting resin in the composite cloth and the composite ratio of fibers will be explained next.

As mentioned above, a laminate with a desired coefficient of linear expansion can be obtained by changing the fiber volume content, but in practical terms, the fiber volume content is preferably 40 to 60% in order to prevent registration. In the case of a combination of resin and aromatic polyamide fiber, the fiber volume content at which a desired coefficient of linear expansion can be obtained may be 40% or less. In this regard, by changing the composite ratio of fibers in a mixed twisted yarn of aromatic polyamide fibers and glass fibers, it is possible to create a laminate with a fiber volume content of 40 to 60% and a desired coefficient of linear expansion.

Next, upon mounting, the appropriate range of linear expansion coefficient of the substrate and the content of the lead wireless semiconductor device to be mounted will be explained below.

The fatigue life of the solder joint of a lead wireless semiconductor device is caused by the repeated strain of the joint solder caused by the difference in thermal expansion between the substrate and the lead wireless semiconductor device and the temperature of the environment in which it is used. For this reason, the appropriate linear expansion coefficient range for the board on which the lead wireless semiconductor device is mounted is such that the strain in the bonding solder is such that the solder does not break during the life required for the lead wireless semiconductor device. Due to the difference in thermal expansion with the non-contact semiconductor device. The lifespan required for the device is determined by the device designer, and the strain that occurs in the solder joint is determined by the following causes.

(a) Difference in thermal expansion between the substrate and the lead wireless semiconductor device, (b) Operating environment temperature; (c) Size of lead wireless semiconductor device and (d) Height and shape of solder joint.

For example, 20mm diagonally (so 14.142mm on a side)
A square ceramic chip carrier with a linear expansion coefficient of 6.4×10 ^-6 K ^-1 is mounted on a substrate with a height h = 0.1 mm.
Bonded with 40Pb ^- 60Sn, power on and off once a day
We will consider a case where a lifespan of 10 years (3650 times) is guaranteed in a usage environment where the temperature change △T = 40°C occurs by repeating the test twice.

The strain at which 40%Pb-60%Sn reaches a life of 3650 cycles is △γ = 0.83%, and the relationship between this strain and the linear expansion coefficient difference △α between the ceramic chip carrier and the substrate is approximately expressed by the following equation (10 ).

△γ=l・△α・△T/h (10) From equation (10), △α=1.5×10 ^-6 K ^-1 , and the linear expansion coefficient of the substrate is 4.9×10 ^-6 to 7.9×10 ^-6 It becomes K ^-1 .

Next, the present invention will be specifically explained by showing examples.

Example 1 Brominated bisphenol A type epoxy resin (epoxy equivalent: 480 g/eq) 90 parts by weight, cresol novolak type epoxy resin (epoxy equivalent: 220 g/eq)
eq) Methyl ethyl ketone and methyl cellosolve were added as solvents to 10 parts by weight, 4 parts by weight of dicyandiamide, and 0.2 parts by weight of benzyldimethylamine to prepare a varnish with a concentration of 37%.

On the other hand, 22.5 tex glass fibers and 21.7 tex poly-P-phenylene terephthalamide fibers are twisted together one by one to make a composite yarn, and this is woven into a composite cloth with a linear density of 37 x 37 yarns/25 mm width. I made it.

Dip this composite cloth into the above varnish,
It was dried at 160°C for 5 minutes to obtain a prepreg. The resin content in this prepreg was 29.5% by weight (approximately 35% by volume).

Next, eight sheets of this prepreg (the coefficient of linear expansion of the prepreg was 5.8×10 ^-6 K ^-1 ) and two sheets of copper foil (thickness 35μ) were placed on top of each other and pressed at 170°C for 60 minutes. A double-sided copper-clad laminate with a thickness of 1.03 mm was created.

A copper wiring pattern was formed by etching the surface copper foil of this copper-clad laminate with a ferric chloride solution, and a double-sided printed wiring board was produced. Therefore, since the copper foil is extremely thin relative to the prepreg layer and is removed leaving a wiring pattern, the coefficient of linear expansion of the substrate can be considered to be substantially the same as that of the prepreg. Solder paste was applied onto the electrode pattern on this double-sided printed circuit board, a chip carrier was placed on this pattern, and the chip carrier was heated to 215°C in the steam of Fluorinert FC70.It was made of alumina with a linear expansion coefficient of 6.4 x 10 approximately 16 mm square. ^-6 K ^-1 chip carrier and double-sided printed circuit board were connected using 40%Pb-60%Sn solder.

Place the double-sided printed wiring board on which the chip carrier is mounted in a temperature cycle test chamber and heat it at 125℃ to -65℃ for 1
A cycle/hour temperature cycling test was conducted.

Fatigue fractures in the soldered joints were detected by resistance measurements and external observations, and the results showed that even after 200 temperature cycles, the soldered joints did not break and the resistance hardly changed.

In addition, when measured according to the peel test method of JISC6481, the interlayer adhesion in the mounting structure is 1.
It was over Kg/cm.

Comparative Example 1 Using the same varnish as in Example 1, glass cloth was impregnated to make a prepreg, and 8 sheets of this prepreg and 2 sheets of copper foil were placed one above the other to create a double-sided copper-clad laminate. A double-sided printed wiring board was created in the same manner as above, and the chip carrier and this double-sided printed wiring board were connected by soldering. According to this, the interlayer adhesion was good at 1 kg/cm or more, but when a fatigue test similar to that in Example 1 was conducted, the solder joint broke after 40 to 50 temperature cycles, and the resistance has become infinite.

Comparative Example 2 40 parts by weight of phenol novolak epoxy resin (epoxy equivalent: 180 g/eq), brominated phenol volak epoxy resin (epoxy equivalent: 285 g/eq)
ep) 60 parts by weight, dicyandiamine 6.4 parts by weight,
A varnish with a concentration of 37.5% was made by adding methyl ethyl ketone and methyl cellosolve to 0.1 part of benzyldimethylamine. A cloth made of poly-P-phenylene terephthalamide fibers was impregnated with this varnish to obtain a coated cloth at a temperature of 160° C. and a coating speed of 1.5 n/min.

Ten sheets of this prepreg and two sheets of 35 μm thick copper foil were stacked together and pressed at 170°C for 1 hour at a pressure of 80 kg/cm ² to create a double-sided copper-clad laminate with a thickness of 0.8 mm.
A double-sided printed wiring board was prepared in the same manner as in Example 1, and the chip carrier and this double-sided printed wiring board were connected by soldering. According to this, in the fatigue test, the solder joint did not break even after 200 temperature cycles as in Example 1, but the interlayer adhesive strength was 0.7 kg/cm.

As can be seen from the above examples and comparative examples,
Comparative Example 1 has a short temperature cycle, and Comparative Example 2 has weak interlayer adhesion, both of which have fatal flaws in terms of practicality. However, in the example, the temperature cycle is 200
It can be seen that the soldered joints do not break even after cycling, and the interlayer adhesion is strong, making it usable for practical use.

As described above, according to the present invention, it has good affinity with the resin used as a matrix, is difficult to peel off at the interface of the cloth in the laminate, has good thermal conductivity, and does not cause registration. It is possible to obtain a lead wireless semiconductor device mounting structure that has high reliability and a temperature life cycle that is difficult to achieve.

[Brief explanation of drawings]

Figures 1 and 2 show the configuration of the mounting structure of a conventional lead wireless semiconductor device.
is a cross-sectional view showing the connection of a flip chip to an alumina substrate, FIG. 1b is a top view of FIG. 1a, and FIG. 2a is a top view of FIG.
2 is a cross-sectional view showing the connection of the chip carrier to the printed wiring board, FIG. 2b is a top view of FIG. 2a, and FIG. , FIG. 4 is a diagram showing the relationship between the volume content of aromatic polyamide fibers and the linear expansion coefficient of the substrate, and FIGS. 5 and 6 are examples of the mounting structure of the leadless semiconductor device of the present invention. 5a is a sectional view showing the connection of the chip carrier to the printed wiring board, FIG. 5b is a top view of FIG. 5a, and FIG. 6a is the connection of the silicon element to the substrate. A cross-sectional view, Fig. 6b is a top view of Fig. 6a, Fig. 7
The figure is a characteristic diagram showing the relationship between the volume content of the composite fiber and the linear expansion coefficient of the laminate. Figure 8 is the volume content of poly-P-phenylene terephthalamide fiber in the composite fiber and the linear expansion coefficient of the laminate. FIG. 8... Laminate board, 9... Copper wiring, 10... Through hole, 11... Chip carrier, 12... Solder, 15... Laminate board, 16... Silicon element, 1
7...Solder.

Claims (1)

[Claims] 1. In a lead wireless semiconductor device mounting structure in which a lead wireless semiconductor device is mounted on a printed wiring board formed by heat-pressing molding of a plurality of prepregs and a plurality of metal wiring layers, the prepreg is heated in a plurality of crosses. The composite cloth is impregnated with a curable resin, and the composite cloth is a woven fabric of composite yarn made by mixing and twisting aromatic polyamide fibers and glass fibers, and the linear expansion coefficient of the lead wireless semiconductor device has the aforementioned printing. A lead wireless semiconductor mounting structure characterized by matching the linear expansion coefficient of the wiring board.