JPS5924543B2 - How to form electrode leads - Google Patents

Description

Detailed Description of the Invention In recent years, as the functions of LSIs have increased, the number of lead terminals derived from the semiconductor elements of LSIs has increased to 40 to 80, and they are no longer connected one by one by AU and At lines as in the past. In the wire bonding method, the time used for bonding increases as the number of electrode terminals increases.
Not only did it increase the cost of the connection, but it also reduced the reliability of the connection.

In order to eliminate these drawbacks of wire bonding,
The general method by which the gang bonding method has been developed and put into practical use will be explained with reference to FIG.

Cu lead formed on polyimide resin film 1 (
A Sn plating layer 2 is formed to a thickness of 0.2 to 0.6 μm.

C on the electrode terminal of the semiconductor substrate 4 (SiO2 film 44)
A metal film 5 (referred to as a barrier metal) consisting of a plurality of materials such as r(u, Th-Cu, etc.) is formed by vacuum evaporation, sputter evaporation, etc., and Au protrusions 6 are further formed on the metal film 5 by electrolytic plating. The Au protrusions 6 are formed to have a thickness of 10 to 201 Lm.The Au protrusions 6 are formed at the positions of the electrode terminals of the semiconductor element by the number of electrode terminals, and the Cu leads on the polyimide resin film are formed at positions corresponding to the electrode terminals. A configured as shown in Figure 1.
The u protrusion 6 and the Cu lead 2 are aligned with each other.
All Cu is heated from the u-lead 2 side using a jig heated to about 480℃.
If lead 2 is pressed at once, Au-Sn eutectic (approximately 28
If the jig is removed, the Au protrusion 6 and the Cu lead 2 will be completely connected. However, although such a connection method using Au/Sn can ensure high connection strength and high reliability, problems occur as shown in FIG. 2, which will be described later. In FIG. 1, diagram b shows a heating jig 50 (for example, a jig that heats only during bonding in a pulsed manner, or a jig that has a built-in heater and is constantly heated).

) descends and pressurizes the Cu lead 2 and the Au protrusion 6, bringing the Cu lead 2 and the Au protrusion 6 into pressure contact. Next, when a pulse current 51 is passed through the heating jig 50, the heating jig 50 instantly reaches a predetermined temperature. At this time, the temperature of the heating jig 50 is increased from the Cu lead 2 to the semiconductor substrate 4 via the Au protrusion 6 having good thermal conductivity.
(arrow 52). Therefore, the temperature of the portion 53 of the Cu lead 2 in contact with the Au protrusion 6 becomes lower than the temperature generated by the heating jig 50, but
Portions 54, 54 of the Cu lead 2 that are not in contact with the protrusion 6
The temperature of ' is approximately equal to the temperature of the heating jig 50.
That is, a temperature difference occurs between the Cu lead portions 53 and 54, 54.

Since this state occurs instantaneously (within about 500 mS), Au-Sn eutectic is generated at the ends 55, 55' of the Au protrusion 6, and then the temperature of this part increases at the top 53 of the Au protrusion 6. It occurs after reaching the Au-Sn eutectic temperature (280°C). However, the eutectic 56 generated on the Au protrusion 6 exists only on the Au protrusion 6 as shown in Fig.
At times, a large amount of the eutectic formed at the ends 55, 55 of the Au protrusions 6, 7 flows down onto the semiconductor substrate 4 as shown in FIGS. 2A and 2B.

This is the cause of cracks caused by eutectics. Therefore, the Sn layer on the Cu lead 2 protruding from the Au protrusion 6 is the cause of cracks. On the other hand, it is easy to consider adjusting the thickness of the Sn plating in order to suppress the amount of eutectic material generated at the ends 55, 55 of the Au protrusions 6 as much as possible.

In general, the amount of eutectic generated is more likely to occur as the Sn plating thickness increases and the temperature of the heating jig 50 increases.

Therefore, it is necessary to control the thickness of the Sn plating and the heating temperature, but the biggest problem is the non-uniformity of the temperature distribution of the heating jig. For example, heating jig 5
The dimensions of the side that pressurizes the Cu lead of 0 are 2.4X6.0?
m (for example, the dimensions of a 4Kbit RAM), in such a small area, the temperature of 480°C is
．． It is extremely difficult to achieve uniformity over the entire 0 m area. At the end of the heating jig, heat radiation is intense and a sharp temperature gradient is exhibited. FIG. 1d shows actual measured values using a 2.4 x 6.0 m pulse tool. If the bonding conditions for generating the initial Au--Sn eutectic were 480 DEG C., it would be fine near the center, but there would be too much temperature difference near the periphery. In order to increase the temperature near the periphery from 415°C to 480°C, the temperature near the center must be at least 550-56°C.
The temperature must be raised to 0°C. In this case, the amount of eutectic produced is extremely large on the Au protrusion near the center of the heating jig, and the excess eutectic flows down onto the semiconductor substrate 4, causing cracks. In addition, in the case of the temperature distribution as shown in Figure 1 d, it is possible to increase the Sn plating thickness and form a eutectic even at a low temperature, but at around 415°C, even if a suitable amount of eutectic is formed, the ℃, the Sn plating is thick, so the amount of eutectic increases accordingly, which results in the occurrence of cracks. That is, even if the Sn plating thickness is adjusted, the temperature distribution of the heating jig cannot be ignored, so this is not a fundamental solution. Fig. 2 AVC}, the Au protrusion 6 and the Cu lead 2 are connected by the Au/Sn eutectic 7', but at the moment the eutectic 7'/) is generated, the red The generated eutectic 7 is SiO2 of the semiconductor substrate 4.
It falls instantaneously onto the film 4'1.

At this time, cracks 8 are instantaneously generated due to the difference in thermal expansion between the SiO2 film 4, the semiconductor substrate 4, or the barrier metal 5. The cracks 8 significantly reduced the tensile strength of the Cu lead 2, and also damaged the P/N junction formed in the semiconductor substrate 4, leading to a decrease in electrical characteristics. In addition, in a configuration where the Au protrusion 6 and the edge of the semiconductor substrate 4 are relatively close to each other, the second
As shown in FIG. b, the eutectic 9 flows out to the edge of the semiconductor substrate 4 and comes into contact with the semiconductor substrate 4 (indicated by arrow 10), causing an electrical short circuit problem. The present invention actively prevents cracks in the semiconductor substrate caused by excess eutectic material and short circuits between the eutectic material and the semiconductor substrate in gang bonding that uses Au-Sn eutectic material for connection. It is an object of the present invention to provide a highly reliable lead formation method that prevents the above problems.

FIG. 3 shows the configuration of the present invention.

After Cu lead 2 is formed on polyimide resin 1, 0
．． Sn plating 3 is applied to a thickness of 2 to 0.8 μm.

The Cu lead 2 is provided at a position that matches the electrode terminal on the semiconductor element 11. To mold the Cu lead, the tip of the Cu lead 2 can be molded into an L-shape as shown in FIG. 3b by pressing a female mold 4 having a concave portion and a male mold 5 having a convex portion. Width A of female mold 4 with recess
is the length B of the opposing Au protrusions 12 and 12 in Fig. 3b.
It is made smaller than. Further, the width C of the male mold 5 having the convex portion is equal to the Cu lead interval D after molding.
The dimension F of the Cu lead 2 after molding is larger than the inner dimension G of the opposing Au protrusions 12, 12', and the dimension H is A.
It is designed to be smaller than the outer dimension B of the u projections 12, 12'. Furthermore, the dimension E between the Cu leads 2 before molding is designed to be smaller than the dimension F after molding. In addition, the BVC diagram in FIG.
The protrusion 12 is formed by Au plating to a thickness of 10 to 20 μm, and is provided on a barrier metal 13 formed of multiple layers of Cr-Cu, Th-Cu, and the like. Figure 3c
In, the dimension 1 of the tip of the molded Cu lead 2 is:
It is formed to be smaller than the dimension J of the Au protrusion 12. For example, if J is 100 μm, I is 70 to 80 μm.
It is formed into m. Furthermore, when positioning the molded Cu lead 2 to the Au protrusion 12, the tip of the molded Cu lead should not protrude from the Au protrusion, and be pressed with a heated jig (approximately 480°C). Then Au-S
The Cu lead 2 and the Au protrusion 12 are connected by generating n eutectic 14. The eutectic 14 is such that the dimension 1 of the formed Cu lead 2 is the length J of the Au protrusion.
Since the Au--Sn eutectic 14 is shorter than the above-mentioned Au protrusion 12, the surplus Au--Sn eutectic 14 is not generated and almost stops on the Au protrusion 12. The eutectic flows out onto the semiconductor substrate, and the deterioration of electrical characteristics due to the generation of cracks in the semiconductor substrate, which conventionally occur, and accidents where the flowing eutectic comes into contact with the semiconductor substrate do not occur. For this reason, highly reliable lead connections can be made.

[Brief explanation of drawings]

Figures 1A, b, and c are cross-sectional views of the structure of the conventional example, Figure d is a diagram showing the temperature distribution, Figures 2A and b are sectional views showing problems caused by bonding in the conventional example, and Figures 3A, b. , c are process sectional views in one embodiment of the present invention. 1...Polyimide resin, 2...Cu lead, 3'...Sn plating, 11...
Semiconductor element, 12, 12...Au protrusion.

Claims (1)

[Claims] 1. In a method of gang bonding an Au protrusion provided on an electrode terminal on a semiconductor element and a Sn-plated Cu lead provided on a resin film tape, the Cu lead is folded in the thickness direction at the tip region in the extending direction. After forming a bent tip region of the Cu lead which is bent to form a step and is in contact with the Au protrusion to be smaller than the length of the Au protrusion, the bent tip region of the Cu lead is formed into the Au protrusion.
A method for forming an electrode lead, characterized in that the electrode lead is formed by gang bonding without protruding from a protrusion.