JPS6142862B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to semiconductor elements such as diodes and transistors, and integrated circuits of these semiconductors (hereinafter referred to as
The present invention relates to a package forming method for airtightly storing semiconductors (referred to as semiconductors), and more specifically, at least one pre-formed lead frame with semiconductors mounted thereon has a recess for storing semiconductors. pieces of thermoplastic resin plate-shaped molded products (hereinafter referred to as
The present invention relates to a method for manufacturing thermoplastic resin flat packages, dual in-line packages, etc., which are made integrally airtight while being sandwiched between plates (referred to as plate-like bodies).

Traditionally, packaging methods for semiconductors include metal,
There are two types of packaging methods: one using ceramics, glass, etc. for an airtight seal, and the other using plastic. Recently, inexpensive plastic packaging has become mainstream due to improved reliability due to advances in chip protection technology.

Currently, there are two types of plastic packages in practical use, the so-called molding method and the injection method, depending on the manufacturing method.

Among these, plastic packages made by transfer molding of epoxy resins, which have excellent adhesion to metals, moisture resistance, and electrical and mechanical properties, are most commonly used.

In this molding method, as shown in FIG. 1, a lead frame 5 in which a semiconductor chip 2 on a tab 1 is connected to a lead 4 using a lead wire 3 made of gold, aluminum, etc. is placed between an upper mold 6 and a lower mold 7. In this method, a molded resin material is filled into the cavity 8 using a transfer molding machine via sprues, runners, and gates (not shown).

This transfer molding method creates a gap between the mold and the lead frame due to variations in lead frame thickness, mold machining accuracy, wear due to use, and dimensional deviations, and flashes occur in and around this area. In many cases, these flashes on the leads cause poor contact between the leads and the sockets and hinder soldering work, so they have to be removed.

Furthermore, this method has disadvantages such as the occurrence of thermal stress due to the difference in coefficient of thermal expansion between the lead frame, lead wires, or semiconductors and the resin material used for sealing, which may cause internal lead wires to break or chips to crack. It was hot too.

In order to improve this drawback of the transfer molding method, as shown in FIG. Although not shown in the figure, a lead frame 5 on which semiconductors are mounted
is sandwiched between the fixed base 10 and the ultrasonic vibrating tool horn 11, and then ultrasonic vibration is applied to melt the material caused by the vibration friction between the plate-shaped bodies 9, 9' and the lead frame 5. A method of packaging semiconductors has been proposed that involves pouring resin into the lead gaps 12 of a lead frame.

However, even with this method, there is a problem that the following defects sometimes occur.

That is, when the ultrasonic welding conditions are set to the extent necessary for the thermoplastic resin plates to fuse together, the elastic vibration energy of the ultrasonic vibration tool horn 11 causes the semiconductor chips 2 and leads shown in FIG. In some cases, a serious defect occurred in which the lead wire 3 connecting between the two was disconnected from the connection point.

In order to reduce the occurrence of such defects, ultrasonic welding conditions are used, for example, to reduce the amplitude of vibration and shorten the vibration time, and to increase the stress at the joint on the joining surface of the plate-shaped bodies to facilitate melting. Attempts have been made to provide melting protrusions for this purpose, or to preheat the plate-shaped body or lead frame in advance, but these methods still do not prevent the lead wire from being disconnected from the connection point. There was a problem that I couldn't do it.

The present invention has been made in view of these points, and its contents will be explained below with reference to FIGS. 3 and 4 showing one embodiment.

FIG. 3 shows a two-dimensional structure having at least one pre-formed recess 13, 13' (an example having two recesses is shown in FIG. 3) for accommodating semiconductors.
A semiconductor chip 2 is attached to the tab 1 by plate-like bodies 9, 9', and the surroundings are fixing jigs 14, 14'.
The lead frame 5, which is fixed by the above, is sandwiched facing each other by the pressing force of the two ultrasonic vibrating tool horns 11, 11'.

These two ultrasonic vibration tool horns 11, 11'
are coupled to vibrators 16 and 16' via fixed horns 15 and 15', respectively, as shown in the diagram of the vibration system in FIG.
16' is excited by a single ultrasonic oscillator 17, and this vibration is transmitted to the ultrasonic vibrating tool horns 11, 1.
1', and the joining surfaces of the plate-like bodies are molten and amalgamated.

At this time, in order to minimize the vibration of the lead frame and thereby protect the fragile contact points of the lead wires, the vibration phase of the two vibrators, each coupled via a fixed horn, can be effectively controlled. It is important to use two ultrasonic vibrating tool horns that are adjusted to the same phase and are opposed to each other.

As a result, the expansion and contraction vibration state of the two ultrasonic vibrating tool horns during vibration is substantially symmetrical with the plane where the lead frame is located as a symmetrical plane.
It is possible to keep the vibration of the lead frame to a minimum level so that the fragile lead wires do not break.

In order to make the vibration phases of two ultrasonic vibrating tool horns the same, it is necessary to vibrate each vibrator with a single ultrasonic transmitter, and also to vibrate each vibrator of the paired vibration system. The main components, such as the vibrator, fixed horn, tool horn, etc., as well as the pressurizing device for pressing the tool horn and the plate-shaped bodies for joining, are maintained in balance as a pair, and the paired vibration system It is necessary to take into account the equipment and conditions so that the two have the same resonant frequency over time.

In addition, the resonant frequency of the vibration system changes from time to time due to various factors, such as heat expansion due to vibration during the joining operation, fluctuations in the pressing load applied via the tool horn due to melting of the joining interface of the plate-shaped bodies, etc. Therefore, in order to always match the oscillation frequency of the ultrasonic transmitter to the resonant frequency of the vibration system during the joining operation, the ultrasonic welding machine uses one vibrator and a fixed horn as shown in the diagram in Figure 4. A detector 18 picks up the vibration state of the vibration system consisting of a tool horn, etc., and transmits it to the oscillator 1
It is necessary to have an automatic frequency tracking function such as a so-called vibration feedback type oscillation system that provides feedback to the oscillator.

Note that providing melting protrusions on the joining surfaces of the plates to facilitate melting, or preheating the plates and lead frames in advance, will ease the ultrasonic welding conditions and eliminate unnecessary leads. This is effective in keeping frame vibration to a minimum.

Preheating conditions vary depending on the material and shape of the plate-shaped body and lead frame, but are generally performed at a temperature and time below the upper limit that does not cause deformation that adversely affects the plate-shaped body.

Furthermore, within the upper limit temperature and time that does not impede the functions of the semiconductors mounted on the lead frame,
In addition, the temperature and time must be below the upper limit at which oxidation and annealing do not occur in the lead frame.

Various types of thermoplastic resins are used in the present invention depending on the characteristics required for each semiconductor package. In addition to electrical and mechanical properties of a certain level or higher, it is also necessary to have moldability of a certain level or higher.

Typical examples include ether resins such as polyphenylene sulfide, polyphenylene oxide, polyether sulfone, polysulfon phenoxy resin, and polyacetal, polyethylene terephthalate, polybutylene terephthalate, and polyarylate. Among the ester resins and polyamide resins, examples include resins with low water absorption, mixtures of these resins, and combinations of these resins with inorganic fillers, mainly glass fibers.

Example Heat distortion temperature (ASTM D-648 18.6Kg/cm ² )
Using polyphenylene sulfide resin at a temperature of 260° C. or higher, two plate-like bodies having the same shape and size and having a recess for accommodating semiconductors as shown in FIG. 3 were molded by injection molding.

On the other hand, a 32μ thick gold lead wire was used between the electrodes and leads of the MOS LSI mounted on the tab, and a fixing jig was used to secure the 16-pin DIP lead frame, which was connected using thermocompression bonding. , two plate-shaped bodies are placed facing each other, and a force of 4 kg/cm ² is applied from the upper and lower surfaces of the sandwiched plate-shaped bodies through two ultrasonic vibrating tool horns that are pressurized from above and below by the same pressurized gas source. I applied pressure.

The ultrasonic fusion machine used has an oscillation frequency of 19.5KHz.
One of the vibration systems has a vibration feedback frequency tracking function, and each vibration system is configured to vibrate with a single oscillation device, and the two vibration systems are adjusted to have substantially the same vibration phase. The ultrasonic tool horns were used facing each other.

Next, ultrasonic oscillation was performed for 0.8 seconds to fuse the two plate-like bodies together by embracing the lead frame.

The obtained semiconductor package had a weight of 5 kg/cm ² , and no red material was found to have entered the package, especially into the recesses, even in the 24-hour pressurized red water immersion test, and it also performed well in the mounting function test. It was confirmed that no breakage of the lead wire occurred.

As explained above, the following effects are achieved in the present invention.

(1) Two ultrasonic vibrating tool horns in which the vibration phases of the vibrating systems vibrated by two vibrators having a common ultrasonic oscillation source are adjusted to substantially the same phase are opposed to each other. By using a double facing type ultrasonic welding machine to join the plate-like bodies by sandwiching the lead frame with semiconductors attached from above and below, it is possible to avoid damaging the fragile lead wires and to maintain water tightness. A semiconductor package with excellent properties was obtained.

(2) By having a recess for storing semiconductors, the conventional problems of internal lead wire breakage and chip cracking caused by thermal stress have been solved.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views showing a conventional semiconductor package molding method, FIGS. 3 and 4 are cross-sectional views and a vibration system diagram showing an embodiment of the present invention, respectively, and FIG. 5 is a cross-sectional view showing a conventional semiconductor package molding method. FIG. 2 is a perspective view of a semiconductor package obtained by the method of the present invention. Explanation of symbols, 1...Tab, 2...Semiconductor chip, 3...Lead wire, 4...Lead, 5...Lead frame, 6...Upper die, 7...Lower die, 8...
Cavity, 9, 9'... Plate-shaped body, 10... Fixing base, 11, 11'... Ultrasonic vibration tool horn, 1
2... Lead gap, 13, 13'... Hollow, 1
4, 14'... Fixing jig, 15, 15'... Fixed horn, 16, 16'... Vibrator, 17... Ultrasonic oscillator, 18... Vibration state detector.

Claims (1)

[Claims] 1 A lead frame on which semiconductors are mounted is sandwiched between two thermoplastic resin plate molded products, at least one of which has a recess for storing semiconductors, and the thermoplastic resin plate molded products are fused together by ultrasonic vibration. In a package molding method for semiconductors, two ultrasonic vibrating tool horns excited by a common ultrasonic oscillator and having substantially the same vibration phase are each formed into two thermoplastic resin plate-shaped molded products. A method for molding packages for semiconductors, which is characterized in that they are joined together by facing each other in contact with each other.