Semiconductor device and process for fabrication thereof

Details Semiconductor device and process for fabrication thereof Semiconductor device and process for fabrication thereof

2001-02-20

2004-04-06

Graybill, David E. (Department: 2827)

Active solid-state devices (e.g., transistors, solid-state diode

Lead frame

C257S676000, C257S783000

Reexamination Certificate

active

06717242

ABSTRACT:

TECHNICAL FIELD
This invention relates to a semiconductor device having a support member such as a lead frame to which a semiconductor die or chip is attached using a die-bonding material and encapsulated with resin, and a process for the fabrication of such a semiconductor device.
BACKGROUND ART
As methods by which semiconductor chips are attached to lead frames, a method has been used in which a die-bonding material is fed onto the lead frame and the semiconductor chip is bonded thereto.
Such a die-bonding material is known to include, e.g., Au—Si eutectics, solders and resin pastes. Of these, Au—Si eutectics have problems in that they are expensive, have a high modulus of elasticity, and require vibration at the bonding portion. The solders have problems in that they can not withstand temperatures equal to or greater than their melting temperature and have a high modulus of elasticity.
As for the resin pastes, silver paste is the most commonly available. Compared with other materials, silver paste is inexpensive, has a high heat resistance reliability and has a low modulus of elasticity. Hence, they are most widely used as bonding materials for the lead frames of ICs and LSIs.
In recent years, there has been a rapid increase in demand for high-density packaging as electronic machinery has been made smaller in size and thickness. In semiconductor packaging, conventional pin insertion packaging has been substituted by surface packaging, which has become the prevailing packaging method suitable for high-density packaging.
In surface packaging, in order to directly solder leads to printed-wiring substrates, packaging is carried out by infrared reflowing, vapor phase reflowing or solder dipping while heating the whole package.
During this packaging, the whole package is exposed to high temperatures of 210° C. to 260° C. Hence, any presence of moisture in the package cause explosive vaporization of the moisture to cause package cracks (hereinafter “reflow cracks”).
Such reflow cracks may cause a great lowering of the reliability of semiconductor packages, bringing about a serious technical problem.
The mechanism by which reflow cracks ascribable to die-bonding materials occur is as follows: During storage of semiconductor packages, (1) die-bonding materials absorb moisture, (2) this moisture is vaporized upon heating when packaged by reflowing and soldering, and (3) vapor pressure thus produced causes breaking or separation of the die-bonding material layers, (4) so that the reflow cracks occur.
While reflow crack resistance of encapsulant has been improved, the reflow cracks ascribable to die-bonding materials provide a serious matter especially in thin-type packaging. Thus, it is strongly sought to improve its reflow crack resistance.
The silver paste, having been most commonly used, tends to cause reflow cracks because it has become difficult with the increase in size of chips to uniformly coat the silver paste on the whole surface requiring area and also because it is pasty itself and therefore tends to cause voids in bonding layers.
DISCLOSURE OF THE INVENTION
The present invention provides a semiconductor device that employs a filmy organic die-bonding material, may cause no reflow cracks and has good reliability, and a process for fabrication thereof.
In the present invention, a filmy organic die-bonding material is used. This filmy organic material is such a filmy material that is mainly made of an organic material such as epoxy resin, silicone resin, acrylic resin, or polyimide resin (including and organic material containing a metal filler or an inorganic material filler added thereto). The filmy organic die-bonding material which has been heated is contact-bonded to a support member such as a lead frame, and a semiconductor chip is placed on the filmy organic die-bonding material and heat is applied to bond the chip. More particularly, resin paste is provided in the form of a film so that die-bonding material is uniformly applied to the bonding portion.
FIG. 1
illustrates an example of a process for fabricating the semiconductor device of the present invention.
The filmy organic die-bonding material
1
is contact-bonded to a die pad
6
of a lead frame
5
on a heating platen
7
by means of a contact press ((b) in FIG.
1
). The contact bonding may preferably be carried out under conditions of a temperature of from 200° C. to 250° C., a press time of from 0.1 second to 20 seconds and a pressure of from 4 gf/mm
2
to 200 gf/mm
2
.
A semiconductor chip
8
is put on the filmy organic die-bonding material
1
stuck to the die pad
6
, followed by heat contact bonding (i.e., die bonding) ((c) in FIG.
1
). The die bonding may preferably be carried out under conditions of a temperature of from 100° C. to 350° C., a bonding time of from 0.1 second to 20 seconds and a pressure of from 0.1 gf/mm
2
to 30 gf/mm
2
. More preferably conditions for die bonding are of a temperature of from 150° C. to 250° C., a bonding time of 0.1 (inclusive) second to 2 seconds and a pressure of 0.1 gf/mm
2
to 4 gf/mm
2
, and the most preferable conditions for die bonding are of a temperature of from 150° C. to 250° C., a bonding rime of 0.1 (inclusive) second to 1.5 (exclusive) seconds and a pressure of 0.3 gf/mm
2
to 2 gf/mm
2
.
Then, the step of wire bonding ((d) in
FIG. 1
follows, and the step of encapsulating the semiconductor chip with resin ((e) in
FIG. 1
) further follows. Thus, the semiconductor device is produced. Reference numeral
9
denotes and encapsulant resin.
For example, the filmy organic die-bonding material of the present invention is prepared by dissolving or dispersing an organic material such as polyimide or epoxy resin and optionally and additive such as a metal filler in an organic solvent to obtains a coating varnish, coating this coating varnish on a carrier film such as biaxially stretched polypropylene film, followed by evaporation of the solvent, and peeling the filmy material from the carrier film. When prepared in this way, a film having self-supporting properties can be obtained.
The present inventors have discovered that the occurrence of reflow cracks in semiconductor device correlates with the properties or characteristics of the filmy organic die-bonding material, and have made detailed studies on the relationship between the occurrence of reflow cracks and the characteristics of the filmy organic die-bonding material. As a result, they have accomplished the present invention.
According to a first embodiment of the present invention, the semiconductor device and the process for its fabrication are characterized in that, in the semiconductor device having a support member to which a semiconductor chip is attached using a die-bonding material and encapsulated with resin, a filmy organic die-bonding material having a water absorption of 1.5% by volume or less is used as the die-bonding material.
According to a second embodiment of the present invention, the semiconductor device and the process for its fabrication are characterized in that, in the semiconductor device having a support member to which a semiconductor chip is attached using a die-bonding material and then encapsulated with resin, a filmy organic die-bonding material having a saturation moisture absorption of 1.0% by volume or less is used as the die-bonding material.
According to a third embodiment of the present invention, the semiconductor device and the process for its fabrication are characterized in that, in the semiconductor device having a support member to which a semiconductor chip is attached using a die-bonding material and then encapsulated with resin, a filmy organic die-bonding material having a residual volatile component in an amount not more than 3.0% by weight is used as the die-bonding material.
According to a fourth embodiment of the present invention, the semiconductor device and the process for its fabrication are characterized in that, in the semiconductor device having a support member to which a semiconductor chip is attached using a die-bonding material and then enc

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