Casing for electronic components

[54] [75]

CASING FOR ELECTRONIC COMPONENTS

Inventors: Sheldon H. Butt, Godfrey, 111.;

Edward F. Smith, III, Madison; F.
Dennis Gyurina, West Haven, both of
Conn.

[73] Assignee: Olin Corporation, New Haven,
Conn.

[21] Appl. No.: 615,606

[22] Filed: May 31,1984

Related U.S. Application Data

[62] Division of Ser. No. 443,793, Nov. 22, 1982.

[51] Int. C1.3 B65D 65/28

[52] U.S. CI 428/35; 428/413;

428/418; 428/76; 264/300; 427/96; 148/6.16;

148/6.15 R

[5 8] Field of Search 428/413, 416, 418, 461,

428/35; 264/300; 427/96; 148/6.5 R, 6.16

[56] References Cited

U.S. PATENT DOCUMENTS

3,541,041 11/1970 Hermann et al 264/300

3,677,828 7/1972 Caule .

3,716,427 2/1973 Caule .

3.728.177 4/1973 Caule .

3.728.178 4/1973 Caule .
3,764,399 10/1973 Caule .
3,833,433 9/1974 Caule .
3,837,929 9/1974 Caule .
3,853,691 12/1974 Caule .
3,940,303 2/1976 Caule .

3.941.627 3/1976 Caule .

3.941.628 3/1976 Caule .

3,944,449 3/1976 Caule .

3,988,284 10/1976 Wurmb et al 264/300

4,136,149 1/1979 Payne 264/300

4,143,024 3/1979 Adelmann et al 264/300

4,264,379 4/1981 Caule .

4,356,233 10/1982 Lange et al 428/413

4,358,552 11/1982 Shimohara et al 428/413

FOREIGN PATENT DOCUMENTS

771127 8/1960 United Kingdom .

1309299 10/1973 United Kingdom .

1510558 1/1975 United Kingdom .

2016807 7/1982 United Kingdom .

2093754 8/1982 United Kingdom .

OTHER PUBLICATIONS

Neighbour et al., "Factors Governing Aluminum Interconnection Corrosion in Plastic Encapsulated Microelectronic Devices", Microelectronics and Reliability, Pergamon Press, Great Britain, vol. 16, 1977, pp. 161-164.

Primary Examiner—George F. Lesmes

Assistant Examiner—E. Rollins Buffalow

Attorney, Agent, or Firm—Howard M. Cohn; Barry L.

Kelmachter; Paul Weinstein

[57] ABSTRACT

A copper plastic laminate is provided having a high bond strength. The copper is selected from the group consisting of copper and copper alloys and has on its surface a uniform glassy-like, substantially pore-free coating of copper phosphate. A plastic encapsulating material containing a mold release agent is adhesively bonded to the copper.

5 Claims, 3 Drawing Figures

10

15

CASING FOR ELECTRONIC COMPONENTS

CROSS REFERENCE TO RELATED
APPLICATION

This application is a Division of U.S. application Ser.
No. 443,793, pending filed Nov. 22, 1982, by Sheldon H.
Butt et al. for Adhesion Primers For Encapsulating
Epoxies.

While the invention is subject to a wide range of applications, it is especially suited for encapsulating electrical leadframes with integrated circuits attached thereto and will be particularly described in that connection.

In the electronics industry, one of the basic types of semiconductor packages used for integrated circuits is the plastic molded package. The package may include a leadframe, having an electronic device attached thereto, molded into an encapsulating plastic. This type 2q of plastic package often has reliability problems created by failures in the plastic to metal bond between the encapsulating plastic and the leadframe. The bond failure provides an avenue through which moisture and other atmospheric contaminants can reach the electric 25 device and cause corrosion problems. Such failures are more fully explained and documented in an article entitled "Factors Governing Aluminum Interconnection Corrosion in Plastic Encapsulated Microelectronic Devices" by Neighbour and White published in Microelec- 30 tronics and Reliability, by Pergamon Press in Great Britain, Volume 16, 1977, pages 161-164.

It is known in the prior art to produce a laminate of copper or copper alloys and plastic film. A laminating adhesive is applied between the metal and plastic film to 35 bond them together. A high bond strength results between the copper or copper alloys and the plastic film due to a phosphate coating provided on the metal. Examples of this are disclosed in U.S. Pat. Nos. 3,677,828, 3,716,427, 3,728,177, 3,728,178, 3,764,399, 3,833,433, 40 3,837,929, 3,853,691, 3,940,303, 3,941,627, 3,941,628, and 3,944,449. However, the plastic film laminate disclosed in these patents do not contain mold release agents as set out in the present invention. Since the adhesive is commonly required only between the film 45 and the metal, there is no reason to use a mold release agent. Further, if a mold release agent were used, it would only decrease the bond strength. The absence of mold release agents is significantly different from the present invention where the mold release agents are 50 definitely required to prevent an encapsulating epoxy from sticking to a mold surface. Unfortunately, the mold release agent also hinders the encapsulant from sticking to an encapsulated metal strip such as a leadframe. The resulting bond between the encapsulant and 55 the leadframe is often deficient and creates an avenue for contaminating an encapsulated electronic element attached to the leadframe.

It is a problem underlying the present invention to provide an encapsulated package for an electrical or 60 electronic component which is highly resistant to atmospheric contamination.

It is an advantage of the present invention to provide a casing for an electrical or electronic component which obviates one or more of the limitations and disad- 65 vantages of the described prior arrangements.

It is a further advantage of the present invention to provide a hermetic casing for an electrical or electronic

component which is substantially resistant to the diffusion of contaminants.

It is a yet further advantage of the present invention to provide a casing for an electrical or electronic component which is relatively inexpensive to manufacture.

Accordingly, there has been provided a casing adapted for containing an electrical or electronic component and a method of producing the casing. The casing includes a copper or copper alloy leadframe. An adhesion primer comprising a uniform, glassy and substantially pore-free phosphate coating is applied to the leadframe. Also, an encapsulating material containing a mold release agent is bonded to the copper leadframe to form a hermetic casing. In addition, the encapsulating epoxy may be adhered to copper or copper alloy material having an adhesion primer thereon whenever a strong bond is required.

The invention and further developments of the invention are now elucidated by means of the preferred embodiments shown in the drawings.

FIG. 1 is a graph of a lap shear strength test of uncoated copper alloys;

FIG. 2 is a graph of a lap shear strength test of coated copper alloys;

FIG. 3 is a graph of a durability test for coated and uncoated copper alloys.

The present invention is primarily concerned with forming a strong bond between copper or copper alloy and an encapsulating epoxy or plastic. This is particularly important in semiconductor leadframe applications where the leadframe and semiconductor attached thereto are encapsulated by an encapsulating epoxy. Semiconductor devices are particularly sensitive to degradation and failure from exposure to moisture and/or penetration of atmospheric pollutants into the package through a path between the encapsulating molding compound and the leadframe. Although this is the primary application described herein, it is within the scope of the present invention to apply the treatment described herein wherever copper or copper alloys are molded into the general class of plastics or epoxies which contain mold release agents. The mold release agent also known as an abherent allows the hardened epoxy to release from the encapsulating mold and minimize redressing the mold after each use. Just as the mold release agent prevents the plastic or elastomer from sticking to the mold wall, it also reduces the strength of the bond between the metal or alloy leadframe and the plastic or elastomer.

The metal or alloy which is used in this invention is preferably copper or copper alloy. Also, this metal or alloy may be in any form such as sheets, strip, or foil.

The metal or alloy is coated with a uniform, glassylike, substantially pore-free phosphate coating. This coating may be in the range of thickness from about 20 to about 100 Angstrom units. It may be applied using various techniques as set forth in the patents enumerated above. For example, the coating may be obtained by applying a phosphoric acid solution containing from about 3.5 grams per liter up to the solubility limit of sodium dichromate ... or potassium dichromate ... or mixtures thereof to the copper alloy material. Normally, the application of the aforementioned solution is by immersion of a sheet or strip of material into a bath of the above-mentioned acid solution.