Active solid-state devices (e.g. – transistors – solid-state diode – Encapsulated
Reexamination Certificate
1993-12-06
2001-02-20
Clark, Sheila V. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Encapsulated
C257S795000, C257S790000
Reexamination Certificate
active
06191492
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic device such as a semiconductor device or the like and a method for manufacturing such an electronic device, specifically to an electronic device and a manufacturing method therefor in which a molding is provided with a protection layer applied over the entire body of the electronic device.
2. Description of the Prior Art
Conventionally, an electronic device such as a semiconductor device or the like is wirebonded and a molding material is applied over the entire body of the electronic device.
Generally, in a plastic molding package, water which reduces the reliability of the electronic device enters the molding from external sources, and has a tendency to collect on the rear or under side of the die of the lead frame. Then this moisture vaporizes quickly when the package is soldered (this generally involves immersion in molten solder at 260° C. for 3 to sec). As a result, the molding which is softened by this heating swells, so that cracks or bulging are induced in the molding itself.
A conventional semiconductor device as shown in
FIG. 1
comprises a lead
35
and a die
35
′, an IC chip
28
die-attached to the die
35
′ and a molding
41
.
The frame die
35
′ is made of metal such as copper, “42 Alloy” or the like, on the surfaces, specifically on the under or reverse side, of which a low class oxide
32
is inclined to be formed during heat treatment at 100° C. to 350° C. when the electronic part
28
is die-attached to the die
35
′ through a paste layer
24
.
For this reason, if the molding process is performed using an organic resin to form a molding
41
immediately after the die-attaching, an extremely easily-peeled oxide layer
32
remains between the molding
41
and the copper or “42 Alloy”. When this electronic device is stored for a long period, the moisture from the air is absorbed by the molding
41
and the moisture is accumulated in the vicinity of the oxide layer
32
. For this reason, it is unable to withstand the sudden thermal shock that occurs when solder is subsequently applied for 3 to 10 sec at 260° C., and cracks
33
,
33
′ are produced in the molding
41
around the periphery of the die
35
′. In addition, the moisture collected on the rear side of the die
35
′ is converted to steam and a void
42
occurs at that point, so that swelling
41
′ (the phenomenon of swelling occurs because the water in the vicinity of the die
35
′ turns to gas as a result of the temperature elevation when solder is applied to the molding
41
on the rear side of the die
35
′) occurs on the under or rear side of the molding
41
. Then, for long time use after it is mounted on a printed-circuit board (PCB), the entry of water and impurities at the location of the cracks induces a deterioration in the characteristics and reliability of the semiconductor device.
In addition, in the prior art, the molding
41
is made from an insulating material of organic resin with a high specific resistance of 1×10
17
&OHgr;cm or greater, therefore, at time of assembling using surface mount technology (SMT), static electricity accumulates on the surface of this insulated molding material through the contact with a jig surface or during storage. When this organic resin is thick, the electric field strength in the mold is relatively small, and the electrostatic discharge damage of the electronic parts does not often occur. However, when the thickness of the molding material is 1.5 mm or less, the strength of the electric field of the static electricity becomes relatively large, and, it can not be ignored from the aspect of guaranteeing the reliability of the electronic parts.
SUMMARY OF THE INVENTION
An object of the present invention is to provide, with due consideration to the drawbacks of such conventional devices, an electronic device in which the decrease in reliability is prevented.
Another object of the present invention is to provide a reliable device wherein an electronic device such as a semiconductor device or the like is wirebonded and molding is applied over the entire body of the electronic device.
Another object of the present invention is to use a non-product gas (a gas which does not decompose to form a film of a solid reaction product) for the plasma process to provide a densified layer, so that the surface of the molding modified into the densified layer, or a densified layer is formed on the surface of the molding.
Another object of the present invention is to prevent the development of cracking and swelling by improving the adherence of the die to the molding or protective film which adhere to the die.
Another object of the present invention is to provide a molding process which is carried out on the entire body of the device has been wirebonded, so that the molding operation provides a densified layer on the surface in order to prevent entry of moisture from external sources into this molding.
In the present invention, there is no protective film formation (final coating) at the wafer level to prevent deterioration caused by water permeating the molding, but instead after the molding process (molding process by an organic resin), this film is provided on the outside of the electronic parts, by a plasma process using inert gas such as argon or a fluorinated gas over the molding after the molding process, or by using silicon nitride, “Diamond-Like Carbon” (DLC, referred to as so because it is carbon with the same sp3 bond as a diamond), or the like over the molding after the molding process.
These objects are achieved in the present invention by the provision of a densified layer after completion of the molding process, which prevents the permeation of moisture into the moldings.
Used as the means for providing this densified layer in the present invention are a method of plasma-hardening the organic resin molding in the vicinity of the surface by means of an argon or the like plasma process conducted on the entire body of the device, and plasma CVD process by which the coating of a silicon nitride film or a DLC film acting as a protective film is formed to prevent moisture permeation into this surface.
In the present invention, an even more reliable electronic device can be fabricated using a plasma process, by covering the entire lead frame and chip with silicon nitride, before forming the molding.
Still another object of the present invention is to provide, with due consideration to the drawbacks of the conventional DIPs, an electronic device in which a decrease in reliability from a localized breakdown in the electronic parts because of static electricity and the occurrence of cracks is prevented.
Another object of the present invention is to provide a manufacturing method for forming, on the surface of the molding, a carbonaceous film of carbon or of a substance including carbon as the main ingredient in order to prevent the breakdown of the inner sections of the electronic parts, and to prevent the permeation of external moisture into the interior of the molding material.
These objects are achieved in the present invention by the provision of a carbonaceous film of carbon or of a substance including carbon as the main ingredient, formed on the surface of the molding after completion of the molding process.
For these purposes, the present invention uses a CVD method, utilizing a carbon compound gas, in the application of a film of carbon, or of a material of which carbon is the main ingredient, which has good heat transfer capabilities and which has superior adhesion to the organic resin molding (referred to as DLC).
In the present invention, a carbonaceous film of carbon or of a substance including carbon as the main ingredient, which has good adherence to the organic resin, is formed to a thickness of 0.05 to 5 &mgr;m, or preferably of a thickness of 0.1 to 1 &mgr;m. In order to form this film, a vacuum is first applied to the electronic device covered with molding to draw off the moisture in t
Hayashi Shigenori
Hirose Naoki
Imatou Shinji
Ishida Noriya
Koyama Itaru
Clark Sheila V.
Costellia Jeffrey L.
Nixon & Peabody LLP
Semiconductor Energy Laboratory Co,. Ltd.
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