Encapsulation method

United States Patent ti?j

Sakai et al.

■■Illllllllllll

US005798070A [ii] Patent Number: [45] Date of Patent:

5,798,070 Aug. 25, 1998

[54] ENCAPSULATION METHOD

[75] Inventors: Kunito Sakai; Kazuharu Oshio;

Hirozob Kanegae. all of Hyogo-ken,
Japan

[73] Assignee: Mitsubishi Denki Kabushiki Kaisha.

Tokyo, Japan

[21] Appl. No.: 609,786
[22] Filed: Mar. 4, 1996

Related U.S. Application Data

[60] Continuation of Ser. No. 358,303, Dec. 19, 1994, abandoned, which is a division of Ser. No. 130,444, Oct 1,1993, Pat. No. 5395,226.

[30] Foreign Application Priority Data

Feb. 23, 1993 [JP] Japan 5-33308

[51] Int CI.6 B29C 33/24; B29C 70/70

[52] U.S. CI 264/272.17; 264/276; 264/DIG. 50;

425/116; 425/DIG. 19; 425/DIG. 47

[58] Field of Search 425/112. 116.

425/543, 544, 588, 117, 121. DIG. 47. DIG. 19; 264/272.17, 276. 313. 314, 275,

DIG. 50

[56] References Cited

U.S. PATENT DOCUMENTS

2,326,381 8/1943 Mffligao et al 264/DIG. 50

2,615,411 10/1952 devenger et al 264/DIG. 50

3,200,442 8/1965 Haller 264/DIG. 50

3,398,222 8/1968 Kaufman, Jr. et al 264/266

4,626,185 12/1986 Monnet.

4,732^53 3/1988 Hofer 425/116

4,952,135 8/1990 Douglas 425/543

A molding machine comprises a mold composed of lower and upper mold sections. A recess is defined in the lower mold section to receive a lead frame or other objects. The lead frame is sandwiched between the upper and lower mold sections. A mold cavity is denned in the lower mold section below the recess so as to receive a thermosetting resin or encapsulant. A gasket groove is defined adjacent to the mold cavity to receive a gasket The gasket is subject to plastic deformation upon application of force. An oil chamber is communicated with the gasket groove and contains hydraulic oil. The hydraulic oil is pressurized to urge the gasket against the lead frame. As a result, the gasket is so deformed as to closely contact the surface of the lead frame and seal the mold cavity. The hydraulic oil is preferably mixed with thermoplastic resin in powder form.

12 Claims, 4 Drawing Sheets