JPS5942977B2 - Manufacturing method of semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and particularly to a wire bonding method.

As is well known, in the manufacturing method of semiconductor devices, integrated circuit devices, etc., small semiconductor pieces (pellets) on which circuit elements are formed are used.
Silver paste, which is a conductive adhesive, is used when fixing a lead frame to a lead frame made of a metal plate because it is inexpensive and can be bonded at low temperatures.

By the way, copper-based lead frames have a much larger thermal expansion coefficient than pellets made of silicon etc. (copper has a thermal expansion coefficient of 17 x 10-6/°C, while silicon has a thermal expansion coefficient of 3 x
10-6/°C.

). Furthermore, since pellet bonding using silver paste requires a process called baking, the pellets and lead frame are heated to a temperature of about 150 to 350° C., although this varies depending on the type of silver paste. Therefore, thermal stress occurs between the pellet and the lead frame, which have returned to room temperature after baking, due to the difference in thermal contraction. This thermal stress acts on the silver bonding layer that connects the pellet and lead frame, but this silver bonding layer consists of silver powder and resin.
Since it is a hybrid with
Cracks occur due to the inability to withstand the thermal stress,
The strength of the silver bonding layer decreases. It was also found that once the strength of the silver bonding layer had decreased, the strength did not increase even if the silver bonding layer was brought to a high temperature again. For example, experimentally, 1.26 mwL
ABLEBOND pellets of 3m recommended on a copper plate with a thickness of
It was fixed using a silver paste called 826-1 (trade name) that does not easily deteriorate even at high temperatures (baked at 350°C for 20 seconds), and then cooled to room temperature of 25°C.
Then perform nail head wire bonding 320
When the bonding strength was measured at a temperature of around 350°C, the bonding strength was extremely low at around 369 (average value) at 350°C, and some of the bonding strengths were less than 18 fl of the tensile strength of a 38 μmφ gold wire. Therefore, when wire bonding is performed with the strength of the silver bonding layer reduced in this way, after fixing one end of the wire to the pellet electrode, the wire is pulled to form a loop, and the other end of the wire is attached to the lead side. When connecting, the tension applied to the wire causes a break in the silver bonding layer,
Pellet peels off from lead frame. on the other hand,
After baking the silver paste, we measured the bonding strength of pellets, etc., which were left without lowering the temperature, and found that the bonding strength was far greater than the tensile strength of the gold wire. For example, the ABLEBON
For D826-1, the average bonding strength at 350°C after baking at 350°C for 20 seconds is 4199.
Therefore, the joint strength is 18f of tensile force of gold wire! The bond strength is approximately 23 times higher than that of the conventional method (3
69) is approximately 11 times larger. The present invention was made in recognition of this fact, and its purpose is to prevent pellets from peeling off from a lead frame during wire bonding.

In order to achieve this purpose, the present invention involves baking the paste layer, keeping the pellets, etc. in the same temperature range as the baking temperature without lowering them to room temperature, and wire bonding in this temperature range. The present invention will be specifically explained below with reference to Examples.

Drawings a to d show an embodiment of a method for manufacturing a semiconductor device according to the present invention. As shown in FIG. 1A, a silver paste layer 3 is applied onto the tab 2 of the copper lead frame 1, and a silicon pellet 4 is placed on top of the silver paste layer 3. Next, figure b
As shown in , the lead frame 1 is placed on the upper left side of the heat block 5 kept at a high temperature and baked.
When using O826-1, bake at 350°C for 20 seconds (baking temperature and time vary depending on the type of silver paste, the processing temperature is 150°C to 350°C, and the processing time is around 20 seconds to 1 hour. ). As a result, the silver paste layer 3 is solidified and becomes the silver bonding layer 6, which has a certain bonding strength (ABLEBONO82
6-1 has a bonding area of 3 mm, the bonding strength is approximately 4209. ). Next, as shown in Figure c, the lead frame 1 is slid to the right on the heat block 5 which is in a high temperature state, and the electrode and lead frame of the pellet 4 are bonded using the nail head wire bonding method at a temperature of 320°C. 1 each lead 7 with gold wire 8 (for example, 3
Connect with 8mmφ gold wire).

Thereafter, as shown in FIG. The semiconductor device 12 is made by cutting.

Incidentally, if necessary, the leads 7 protruding from the resin mold part 9 may be bent in a certain direction to form a dual in-line type semiconductor device.

According to this manufacturing method, after the silver paste is baked and solidified, wire bonding is performed without lowering the temperature. As a result, the thermal stress caused by the difference in thermal expansion coefficient between the pellet and the lead frame is small, and no cracks or the like occur in the silver bonding layer. Therefore,
The bonding strength of the silver bonding layer maintains a much greater strength than the tensile strength of the gold wire. Therefore, the silver bonding layer is hardly ruptured by the tensile force applied to the wire after the wire is bonded to the pellet and before the wire is connected to the lead. Furthermore, even if a crack occurs in the silver bonding layer after wire bonding, it can be tightened at the resin mold part by molding with resin.
There is no problem. Note that the present invention is not limited to the above embodiments. That is, the paste may be gold paste or other insulating paste. Further, the wire bonding method may be other than the ultrasonic wire bonding method. Further, after baking, it may be placed in a high temperature constant temperature bath, and then wire bonding may be performed inside or outside the constant temperature bath without lowering the temperature. As described above, according to the method for manufacturing a semiconductor device of the present invention, wire bonding is performed without reducing the bonding strength (bonding strength) of the silver bonding layer. It will not peel off.

Therefore, yield can be improved.

[Brief explanation of the drawing]

Drawings a to d are process diagrams showing one embodiment of the method for manufacturing a semiconductor device of the present invention. 1...Lead frame, 2...Tab,
3... Silver paste layer, 4... Pellet, 5... Heat block, 6... Silver bonding layer, 7... Lead, 8 ...Gold wire, 9
...Lujin Mold Department, 10...Dam,
11... Tie bar 12... Semiconductor device.

Claims (1)

[Claims] 1. A semiconductor pellet is superimposed on a lead frame made of a metal having a larger coefficient of thermal expansion than a semiconductor via a conductive paste layer, and the paste layer is baked to bond the pellet to the lead frame. A semiconductor device manufacturing method including a pellet bonding step for fixing the pellet, and a wire bonding step for connecting the electrode of the pellet to a lead of a lead frame with a metal wire, the pellet etc. being heated near room temperature following baking in the pellet bonding step The temperature is maintained at a relatively high temperature that does not cause a decrease in the strength of the bonding layer without lowering the temperature to
A method for manufacturing a semiconductor device, characterized in that wire bonding is performed in this state. 2. The semiconductor device according to claim 1, wherein after baking the paste layer, the temperature is maintained at around 320° C., and wire bonding is performed by a nail head method (thermo-compression bonding method) under this temperature condition. manufacturing method.