JPH03290956A - Lead frame material for plastic package - Google Patents

Abstract

PURPOSE:To enable reduction of warp or the like on the base side at the time when a semiconductor chip is mounted and heated, and thereby to prevent a damage of the chip such as exfoliation or cracking, by cladding a leaf of a metal of low thermal expansion in the shape of a spot partially on the rear side of a surface whereon the chip is to be mounted. CONSTITUTION:A leaf 11 of a metal material of low thermal expansion having prescribed dimensions is bonded and arranged at prescribed intervals on the necessary surface side of a strip-shaped Cu base material 10 constituted of copper or a copper alloy, so that a spot-shaped partial clad material be constructed. In more detail, the strip-shaped Cu base material 10 is die-cut into a plurality of lead frames of a necessary pattern in the longitudinal direction thereof. Then, the leaf 11 having prescribed dimensions is welded with pressure at positions in the longitudinal direction of the base material 10 whereat islind parts are to be formed, and on a surface on the rear side being reverse to a surface on the side whereon a semiconductor chip is to be mounted, and it is arranged at prescribed intervals in the longitudinal direction. According to this constitution, radiation of heat is very excellent and, moreover, warp on the base side at the time of heating is very small since the necessary leaf 11 is welded with pressure on or buried in the rear side of each island part whereon the chip is to be mounted. Thus, prevention of exfoliation of a bonding interface of the chip with the island is enabled and reliability can be improved.

Description

[Detailed Description of the Invention] Field of Application This invention provides a semiconductor package sealed with plastic that has excellent heat dissipation properties when a large-capacity semiconductor chip is mounted, and has a thermal expansion coefficient that is similar to that of the chip. Regarding the Cu-based lead frame material that prevents chip damage due to alignment, low thermal expansion metal foil is partially clad in spots on the back side of the surface where the semiconductor chip is to be mounted on the Cu-based lead frame material, resulting in excellent heat dissipation. This invention relates to lead frame materials for plastic packages that improve thermal bonding properties with large-capacity semiconductor chips made of Cu-based materials, reduce warping of substrates during chip mounting heating, and prevent chip damage such as peeling or cracking. .

Background Art Integrated circuit chips (hereinafter referred to as chips) in semiconductor packages, especially LSIs and ULSIs for large computers,
The trend is toward higher integration and faster calculation speeds, and the amount of heat generated during operation is increasing due to increased power consumption.

In other words, chips have become larger in capacity and generate more heat, and if the coefficient of thermal expansion of the substrate material is significantly different from that of the chip material, such as silicon or gallium arsenide, there is a problem that the chip may peel off or crack. .

Along with this, the design of semiconductor packages has also begun to take heat dissipation into consideration, and the substrate on which the chip is mounted is also required to have heat dissipation, and the substrate material is required to have high thermal conductivity. There is.

In a resin-sealed semiconductor package as shown in Figure 6, the lead frame not only serves as a route for electrical connections to the outside of the chip, but also plays an important role as a dissipation route for the heat generated in the chip. .

In other words, in a plastic package, a chip (2) is placed on an island (11) formed in the center of a lead frame (1), and is fixed with brazing material, adhesive, solder, etc., and is connected to internal leads. (12) and is electrically connected via a bonding wire (3), and the periphery is further sealed with resin (4).

The heat generated from the chip (2) is transferred to the island (1□),
It reaches the external lead (13) of the lead frame (1) through the resin (4) and internal lead (12), and the resin (4)
) will be dissipated to the outside together with the outer surface.

Therefore, a material with good thermal conductivity is desired for the lead frame (1) in order to dissipate the heat generated from the chip to the outside of the semiconductor package.

As described above, from the viewpoint of heat dissipation, lead frames made of copper alloys with good thermal conductivity have been widely used as lead frames in plastic semiconductor packages.

However, for applications that require high reliability, copper alloys are
Due to poor consistency in thermal expansion coefficient with the chip, there are concerns about peeling of the adhesive interface between the chip and the island, cracking of the chip, etc. Therefore, 42%Ni-
Semiconductor packages employing Ni--Fe alloys having a low coefficient of thermal expansion, such as Fe alloys, have also been proposed.

However, since Ni--Fe alloys have poor thermal conductivity, they do not have sufficient heat dissipation properties to meet current requirements. In addition, the difference in thermal expansion between the chip and the encapsulating resin is very large. It was difficult to completely prevent cracks from occurring in the steel.

Purpose of the Invention In view of the above-mentioned problem of inability to achieve thermal compatibility with a Cu-based lead frame material with a chip in a plastic package, the present invention proposes a method of combining a large-capacity semiconductor chip made of a Cu-based material with excellent heat dissipation properties. The purpose of the present invention is to provide a lead frame material for plastic packages that has improved thermal bonding properties, reduces warping of the substrate during heating for mounting a chip, and prevents chip damage such as peeling or cracking.

Summary of the Invention This invention was made by conducting various studies on the curvature of the island portion during heating when mounting the chip, with the aim of improving thermal bonding between a copper or copper alloy plate that has excellent heat dissipation properties and a large-capacity chip. As a result, by partially cladding the back side of the surface where the semiconductor chip is planned to be mounted with low thermal expansion metal foil in the form of spots, it is possible to reduce warpage on the board side during chip mounting heating, and to prevent chip damage such as peeling or cracking. This is what I found out.

That is, the present invention provides a lead frame material made of a strip-shaped copper or copper alloy plate used for a plastic package in which a semiconductor chip is mounted on an island portion of a lead frame formed by processing such as punching from a strip-shaped substrate material and sealed with resin. The method is characterized in that it is a spot-shaped partial cladding material in which low thermal expansion metal foils of a predetermined size are pressure-bonded to the surface of each island portion in the longitudinal direction of the substrate and on which no semiconductor chip is mounted and arranged at predetermined intervals. It is a lead frame material for plastic packages.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view of a lead frame material according to the present invention. FIGS. 2a, 2b, and 2c are longitudinal sectional views showing a low thermal expansion metal foil clad with a lead frame material according to the present invention. FIG. 3 is a perspective explanatory view showing an example of a low thermal expansion metal material foil used in the present invention. Figure 4 a, b
, c are vertical cross-sectional views of a plastic package using the lead frame material according to the present invention. FIG. 5a is a graph showing the relationship between the thickness ratio of the low thermal expansion metal stamped foil for cladding and the substrate material and the curvature coefficient, and is a perspective explanatory view of the test material.

As shown in FIG. 1, the lead frame material according to the present invention is a strip-shaped Cu-based substrate material (10
) is stamped with low thermal expansion metal foil (11
) are bonded and arranged at predetermined intervals.

To be more specific, lead frames with a plurality of required patterns are punched and formed in the longitudinal direction of the strip-shaped Cu-based substrate material (10) J, and at each island portion planned position in the longitudinal direction of the Cu-based substrate material (1o). , and on the back side surface opposite to the mounting side surface of the semiconductor chip, low thermal expansion metal stamping foils (11) of a predetermined size are pressed and arranged at predetermined intervals in the longitudinal direction.

As will be described later, the low thermal expansion metal stamping foil (11) has a thickness and dimensions selected in consideration of the thickness of the Cu-based substrate material (10), the dimensions of the chips to be mounted, and the like.

In addition, the pressure contact state with the Cu-based substrate material (lO) is shown in Figure 2a.
, b, and c, in addition to pressure-welding the low thermal expansion metal stamping foil (11) to the surface of the Cu-based substrate material (10), it may also be partially or entirely embedded in the substrate material side and pressure-welded. .

In addition, if the low thermal expansion metal stamping foil (11) itself is a so-called punching metal with holes of various shapes as shown in Figure 2C, the Cu-based substrate material will be inserted into the holes, and the copper or copper alloy and low heat Depending on the volume ratio of the expanding metal material, any thermal expansion coefficient value between copper or copper alloys and low thermal expansion metal materials can be selected.

Furthermore, as shown in FIG. 3, the low thermal expansion metal stamping foil (11) has, for example, a copper or copper alloy plate (20) with a large number of through holes (22) in the thickness direction on at least one main surface thereof. The expansion metal plate (21) is integrated by pressure welding, and copper or copper alloy flows through the through hole (22) into the low thermal expansion metal plate (21).
By configuring it to be partially exposed on the surface and selecting the volume ratio of copper or copper alloy and low thermal expansion metal material, an arbitrary thermal expansion coefficient value between copper or copper alloy and low thermal expansion metal material was selected. Metal materials can be used. Moreover, other metal materials can also be used in place of the copper or copper alloy forest.

Materials In addition to pure Cu, the Cu-based substrate material (10) also includes Cu.
-8n system, Cu-Fe system, Cu-Zn system, Cu-Co system, Cu-Ni system, Cu-Zr system, etc., or any of the known Cu alloys in which P, Cr, etc. are added to the Cu system. can also be adopted, and can be selected as appropriate depending on the application, required performance, etc.

The low thermal expansion metal stamping foil (11) includes Ni-Fe alloys with various compositions such as 36Ni-Fe alloy, 31Ni-4Co-Fe alloy, and 42Ni-Fe alloy, as well as so-called Kovar alloy, Mo, Fe- Known low thermal expansion metals such as Cr alloys can be used.

Hirotama Sakuri Using various lead frame materials according to the present invention shown in FIGS. 2 a, b, and c, lead frames having a plurality of desired patterns in the longitudinal direction are formed by punching, for example, and the resulting lead frames are When a plastic package is made using the above steps, the chip (2) is attached to an island (
11) and fixed with brazing material, adhesive, solder, etc., and the internal lead (12) and bonding wire (3)
They are electrically connected via the 3-layer 3-layer connector and the periphery thereof is sealed with resin (4).

In the example shown in FIG. 4a, a low thermal expansion metal stamping foil (11) is placed on the back side of the island (11) on which the chip (2) is mounted.
) are pressure-welded, and in the same figure, the low thermal expansion metal stamping foil (11) is completely embedded in the island (11) part and has the same thickness as the other lead parts. Now let's look at punched foil (a low thermal expansion metal material with a punched metal structure).
11) is embedded in the island (11).

In any of the packages shown in Figures 4a, b, and c, the heat generated from the chip (2) is transferred to the island (11).
, the resin (4), and the internal lead (12) to reach the lead part (13) of the lead frame (1) and dissipate to the outside, but since this entire path is made of Cu-based substrate material, the heat is Extremely good dissipation.

Furthermore, an island (11) on which a chip (2) is mounted
Now, place the required low thermal expansion metal material box (11) on the back side.
Because it is pressure-bonded and embedded, there is very little warping when heated, and it is possible to prevent peeling of the adhesive interface between the chip (2) and the island (11), making it a highly reliable plastic material. You will get a package.

Gogeki Yuta The lead frame material according to the present invention, as shown in Fig. 1, is a strip-shaped Cu-based substrate material (10
), a low thermal expansion metal material box (11) having a material, thickness, and dimensions selected in consideration of the thickness of the Cu-based substrate material (10) and the dimensions of the chips to be mounted, etc., is stacked and pressure-welded and rolled into a predetermined shape. This is spot-shaped partial cladding material arranged at intervals.

In order to select the specific thickness and dimensions of the low thermal expansion metal material box (11), it is mainly confirmed by a mounting test, but the following method can be adopted as a rough guide.

The island part of the lead frame on which the chip is mounted is
Consider the chip and lead frame (substrate material + low thermal expansion metal box) as a composite material, and find conditions under which the composite material will not bend. In other words, the amount of curvature when heated with a temperature difference ΔT is
Find the conditions under which the amount of curvature of the low thermal expansion material on both sides of the substrate material is the same.

In the case of composite materials, the amount of curvature is proportional to the curvature coefficient, so
Find the conditions under which the curvature coefficients are the same.

Therefore, considering the relationship between the curvature coefficient and plate thickness ratio of each combination of the chip and the substrate material, and the substrate material and the low thermal expansion metal material box,
The thickness of the low thermal expansion metal foil may be determined depending on the chip to be mounted and the thickness of the Cu-based substrate material.

As an example, the curve ■ in Figure 5a shows the curvature coefficient of the silicon chip (thermal expansion coefficient 17 x 10') and the Cu-based substrate material, and the curve ■■ represents the curvature coefficient of the Cu-based substrate material + 36Ni-F- Curvature coefficients are shown, and curve (2) shows the curvature coefficient of Cu-based substrate material + Kovar material (thermal expansion coefficient 7 to 8xlO').

For example, as shown in the example, the silicon chip thickness is 0.
4mm, 36N if the Cu substrate material thickness is 0.1mm
It can be seen that the optimal thickness is 0.34 mm or 0.04 mm for the i-Fe material, and 0.1 mm for the Kovar material.

Thermal expansion coefficient α calculated by curvature coefficient α Shishi As mentioned above, the material length = L, the composite material plate thickness = a low thermal expansion metal material box having the material, thickness, and dimensions selected in consideration of the type and thickness of the Cu-based substrate material, the dimensions of the chip to be mounted, etc. The low thermal expansion metal material box is overlapped, pressure bonded and rolled until the required thickness ratio is achieved, but the low thermal expansion metal material box is partially clad in spots in the longitudinal direction of the Cu-based substrate material.
When processing into a lead frame, it is necessary to have highly accurate pitch and dimensions.

In order to obtain a spot-shaped partial cladding material having highly accurate pitch and dimensions, for example, the metal material box unwound from a coil and fed to a fixed length and the Cu-based substrate material are continuously ultrasonically welded at predetermined intervals to temporarily form a temporary cladding material. After fixing, cut the metal foil at predetermined intervals with a pair of rotating cutters and remove the pieces of metal foil that are not fixed.
Alternatively, a metal material box fed to a fixed size is sandwiched and cut with a punch, and at the same time, the metal material box fed to a fixed size is temporarily fixed by spot welding with an electrode built into the punch on the Cu-based substrate material fed to a fixed size. It is preferable to perform ultrasonic welding using a vibrating plate for sonic welding to temporarily fix the parts, followed by pressure welding and rolling.

In addition, after temporarily fixing the metal material box and the Cu-based substrate material sent to a fixed length at predetermined intervals by continuous laser welding, cut the metal stamping foil at predetermined intervals with a rotary cutter to remove the metal foil that is not fixed. Either the piece is removed, or the metal stamped foil that has been fed to a fixed length is sandwiched and cut with a punch, and at the same time, it is temporarily fixed by laser welding while pressing with a punch onto the Cu-based substrate material that is fed to a fixed length, and then it is pressed and rolled. At this time, the rolling load can be controlled by installing a device and a plate thickness gauge to detect the load when pressurizing the unwound Cu-based substrate material by bringing a backup roll into contact with a pair of work rolls of the rolling mill. The equipment calculates the target rolling load by determining the quantitative relationship between rolling load variation, pitch and absolute position variation, and control model based on the measured absolute position of the metal foil piece from the required origin. death,
By performing constant load control, high precision pitch control can be achieved.

(Patent application No. 1-102316, Patent application No. 1-216758
No., Japanese Patent Application No. 1-216759, Japanese Patent Application No. 1-21676
(Refer to No. 0) In addition to the above-mentioned manufacturing methods using pressure welding and rolling mills, the metal foil pieces can also be embedded and arranged in the Cu-based substrate material using a press machine.

Further, the low thermal expansion metal material foil (11) is a Cu-based substrate material (1
0) by a so-called pin-down method, the above-mentioned bending prevention effect is the same, and as shown in Figure 2, the low thermal expansion metal foil (11) is attached to the Cu-based substrate material (10). Even if the metallic stamped foil (11) is only sandwiched between the two thickness ends when it is embedded in the back surface of the position, the above-mentioned warping prevention effect is the same.

The chip mounting surface side of the lead frame material according to this invention,
In other words, Ag or Au plating can be applied in stripes or spots on required surface positions including the bonding area of the lead frame.

Similarly, depending on the type of bonding wire, Ag
Pressure bonding of foil, Au foil, At foil, Cu foil, etc. in stripes,
Alternatively, the above-mentioned method of cutting into foil pieces and temporarily fixing them, then pressing and rolling them can be used to partially clad the various metal foils mentioned above in a spot shape, and the low thermal expansion metal material of the present invention can be used. In addition to partially cladding the front and back surfaces at the same time when the foils are stacked and pressure-welded, it is also possible to partially clad the front and back surfaces separately at different times. After fixing, it can be looped and turned over, and Ag foil or the like can be temporarily attached to the bonding area, followed by pressure bonding and rolling.

Furthermore, by cold or warm welding one or more stripes of pure U-foil with a purity of 99.9% or higher to a thickness of 2 to 50 pm to the surface position including the bonding area of the lead frame, There is no need for expensive Au or Ag spot plating on the Cu alloy lead frame material, which has excellent heat dissipation properties, and Cu wire can be used for bonding in the assembly process, and bonding can be easily and reliably performed.

A preferable pressure welding method is, for example, a method in which after surface cleaning with a softening wire brush, the two are cold pressure welded, and further, after diffusion annealing, rolling is performed to a required thickness. In addition, considering that the pure Cu foil surface maintains the characteristics of pure Cu with a purity of 99.9% or more, maintains good bonding properties, and maintains high mechanical strength, it is necessary to have a thickness exceeding 104. is preferred.

Examples Example 1 In order to punch and mold eight lead frames for a 26-pin plastic package that can mount a chip with dimensions of 15.6 x 6.24 x O and 4 (thickness) mm, 0.0 mm was used.
Pure Cu with dimensions 2x36.5x230mm (txwxl)
A lead frame material consisting of a substrate material was manufactured.

That is, as shown in FIG. 4a, in order to create a configuration in which the low thermal expansion metal foil (11) is pressure-welded to the back side of the island (1□), since m=5silScu=2, the fifth
From figure a, K=9.5, SM/SCu=m=0.8, n
= 1.33, α = 4xlO', E = 15000, and the low thermal expansion metal material foil has a thickness of 0.16 mm or 3.4
36Ni-Fe material with only mmJFi is optimal.

Therefore, 36Ni-Fe material was pressure-welded and rolled to 8 locations of the pure Cu substrate material so that the thickness ratio was as described above, and each part had a thickness of 14.5
A lead frame material was produced in which stamped foil of a low thermal expansion metal material with a size of 5.4 mm and a thickness of 0.16 mm or 3.4 mm was arranged in spots.

When 50 plastic packages were made using the above lead frame material and subjected to a mounting test, there was no chip damage such as peeling or cracking.

Leaving! In Example 1, in order to make the low thermal expansion metal stamping foil (11) shown in FIG. 4 embedded in the island (11) part and have the same thickness as other lead parts, /
Since SCu = 4 and the pure Cu substrate material thickness is set to 0.1 mm, and K = 7.5, the thickness of the island (11) is 0.2 mm from Figure 5a, so SMIScu
=m=1, n=1.33, a=7x10-6, E=15
000, and 0.1mm for low thermal expansion metal stamping foil.
Thick Kovar material is optimal.

Therefore, Kovar material was pressure-welded and rolled to 8 locations of the pure Cu substrate material so that the thickness ratio was as described above, and each part was 14.4 x 5.
A lead frame material was produced in which stamped foils of low thermal expansion metal having a size of 2 mm and a thickness of 0.1 mm were arranged in spots.

When 50 plastic packages were made using the above lead frame material and subjected to a mounting test, there was no chip damage such as peeling or cracking.

As in Example 2, the Kovar material is used as a punching metal and is embedded into the pure Cu substrate material to a thickness of 0.1 mm.
When the lead frame material was pressed and rolled, the Cu substrate material filled the punched holes in the Kovar material during pressure bonding, so the shape of the plate after pressure bonding was very good. Using the above lead frame material, 50 plastic packages were made. When it was created and tested, there was no chip damage such as peeling or cracking.

Effects of the Invention The lead frame material according to the present invention, which is partially clad with a low thermal expansion metal foil in spots on the back side of the surface on which the semiconductor chip is to be mounted, is made of a Cu-based substrate material, and therefore has excellent heat dissipation. The sex is extremely good, and furthermore,
Since the required low thermal expansion metal stamping foil is pressure-bonded and embedded on the back side of the island section where the chip is mounted, there is very little warping when heated, preventing peeling of the adhesive interface between the chip and the island. can be prevented and a highly reliable plastic package can be obtained.

[Brief explanation of drawings]

FIG. 1 is a perspective explanatory view of a lead frame material according to the present invention. FIGS. 2a, 2b, and 2c are longitudinal cross-sectional views showing a low thermal expansion metal stamping foil clad with a lead frame material according to the present invention. FIG. 3 is a perspective explanatory view showing an example of a low thermal expansion metal stamping foil used in the present invention. FIGS. 4a, 4b and 4c are longitudinal sectional views of a plastic package using the lead frame material according to the present invention. FIG. 5a is a graph showing the relationship between the thickness ratio of the low thermal expansion metal stamping foil for cladding and the substrate material and the curvature coefficient,
The figure is a perspective explanatory view of the test material. FIG. 6 is a longitudinal cross-sectional view of a conventional plastic package. 1...Lead frame, 11...Island, 12
...Internal lead, 13...External lead, 2...Chip, 3...Bonding wire, 4...Resin, 1
0...Cu-based substrate material, 11...Low thermal expansion metal material stamping foil, 20...Copper or copper alloy plate, 21...Low thermal expansion metal plate, 22...Through hole. Appearance Sumitomo Special Metals Co., Ltd. Figure 3 Figure 4 (a) (b) (C)

Claims (1)

[Scope of Claims] 1. A lead frame material made of a strip-shaped copper or copper alloy plate used for a plastic package in which a semiconductor chip is mounted on an island portion of a lead frame formed from a strip-shaped substrate material and sealed with resin, It is characterized by being a spot-shaped partial cladding material in which low thermal expansion metal foils of a predetermined size are pressure-welded to the surface where no semiconductor chip is mounted and arranged at predetermined intervals at the planned positions of each island portion in the longitudinal direction of the substrate material and on the surface where no semiconductor chip is mounted. Lead frame material for plastic packages.