Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-07-08
2001-11-13
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S434000, C523S456000
Reexamination Certificate
active
06316528
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to underfilling sealing resin compositions useful for mounting onto circuit board semiconductor devices, such as chip size or chip scale packages (“CSPs”), ball grid arrays (“BGAs”), and the like, each of which having a semiconductor chip, such as large scale integration (“LSI”), on a carrier substrate.
2. Brief Description of Related Technology
In recent years, the popularity of small-sized electronic appliances, such as camera-integrated video tape recorders (“VTRs”) and portable telephone sets, has made size reduction of LSI devices desirable. As a result of these reduction desires, CSPs and BGAs are being used to reduce the size of packages substantially to that of bare chips. Such CSPs and BGAs improve the characteristics of the electronic device while retaining many of their operating features, thus serving to protect semiconductor bare chips, such as LSIs, and facilitate testing thereof.
Ordinarily, the CSP/BGA assembly is connected to electrical conductors on a circuit board by use of a solder connection or the like. However, when the resulting CSP/BGA/circuit board structure is exposed to thermal cycling, the reliability of the solder connection between the circuit board and the CSP/BGA often becomes suspect. Recently, after a CSP/BGA assembly is mounted on a circuit board, the space between the CSP/BGA assembly and the circuit board is often now filled with a sealing resin (often referred to as underfill sealing) in order to relieve stresses caused by thermal cycling, thereby improving heat shock properties and enhancing the reliability of the structure.
However, since thermosetting resins are typically used as the underfill sealing material, in the event of a failure after the CSP/BGA assembly is mounted on the circuit board, it is very difficult to replace the CSP/BGA assembly without destroying or scrapping the structure in its entirety.
To that end, techniques for mounting a bare chip on a circuit board are accepted as substantially similar to the mounting of a CSP/BGA assembly onto a circuit board. One such technique, disclosed in Japanese Laid-Open Patent Publication No. 102343/93, involves a mounting process where a bare chip is fixed and connected to a circuit board by use of a photocurable adhesive, where, in the event of failure, this bare chip is removed therefrom. However, this technique is limited to those instances where the circuit board includes a transparent substrate (e.g., glass) which permits exposure to light from the back side, and the resulting structure exhibits poor heat shock properties.
Japanese Laid-Open Patent Publication No. 69280/94 discloses a process where a bare chip is fixed and connected to a substrate by use of a resin capable of hardening at a predetermined temperature. In the event of failure, this bare chip is removed from the substrate by softening the resin at a temperature higher than the predetermined temperature. However, no specific resin is disclosed, and there is no disclosure about treating the resin which remains on the substrate. Thus, the disclosed process is at best incomplete.
As pointed out in Japanese Laid-Open Patent Publication No. 77264/94, it is conventional to use a solvent to remove residual resin from a circuit board. However, swelling the resin with a solvent is a time-consuming process and the corrosive organic acid ordinarily used as the solvent may reduce the reliability of the circuit board. Instead, that disclosure speaks to a method for removing residual resin by irradiation with electromagnetic radiation.
Japanese Laid-Open Patent Publication No. 251516/93 also discloses a mounting process using bisphenol A type epoxy resin (CV5183 or CV5183S; manufactured by Matsushita Electric Industrial Co., Ltd.). However, the removal process so disclosed does not consistently permit easy removal of the chip, the curing step is lengthy at elevated temperatures, and the process generally results in poor productivity.
Accordingly, it would be desirable for an underfilling sealing material to provide good productivity and thermal shock properties, while allowing the substrates with which it is used to be readily processed and easily separated.
SUMMARY OF THE INVENTION
The present invention provides a thermosetting resin composition useful as an underfilling sealing resin. The composition enables a semiconductor device, such as a CSP/BGA assembly which includes a semiconductor chip mounted on a carrier substrate, to be securely connected to a circuit board by short-time heat curing and with good productivity, which demonstrates excellent heat shock properties (or thermal cycle properties), and permits the CSP/
2
GA assembly to be easily removed from the circuit board in the event of semiconductor device or connection failure.
The thermosetting resin composition which is used as a sealer underfilling between such a semiconductor device and a circuit board to which the semiconductor device is electrically connected, includes about 100 parts by weight of an epoxy resin, about 3 to about 60 parts by weight of a curing agent, and about 1 to about 90 parts by weight of a plasticizer.
Although the thermosetting resin composition of the present invention is curable at a relatively low temperature in a short period of time, cured reaction products thereof have excellent heat shock properties and, moreover, can be easily split by the application of force under heated conditions. That is, semiconductor devices attached to circuit boards and the like by cured reaction products of the thrmosetting resin compositions of this invention can be easily removed by heating the reaction product, allowing it to swell with a solvent, or allowing it to swell with a solvent under heated conditions.
By using the thermosetting resin compositions of this invention, semiconductor devices, such as CSP/BGA assemblies, can be securely connected to a circuit board by short-time heat curing and with good productivity, with the resulting mounting structure demonstrating excellent heat shock properties (or thermal cycle properties). Moreover, in the event of failure, the semiconductor device can be easily removed. This makes it possible to reuse the semiconductor device or circuit board and thereby achieve an improvement in the yield of the production process and a reduction in production cost.
The benefits and advantages of the present invention will become more readily apparent after a reading the “Detailed Description of the Invention”.
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Iida Kazutoshi
Wigham Jon
Aylward D.
Bauman Steven C.
Dawson Robert
Loctite (R&D) Limited
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