Browse Prior Art Database

Attachment of Protective Caps

IP.com Disclosure Number: IPCOM000087155D
Original Publication Date: 1976-Dec-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Gibney, JT: AUTHOR [+3]

Abstract

Fig. 1 shows a large-scale integration (LSI) chip 1 and cooling stud 2. After the chip has been electrically and physically attached to substrate 3, hermetic protective cap 4, made of gold-plated KOVAR*, is secured to said substrate with its gold-plate lamination 4-1 in thermal-conduction contact with the stud.

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Attachment of Protective Caps

Fig. 1 shows a large-scale integration (LSI) chip 1 and cooling stud 2. After the chip has been electrically and physically attached to substrate 3, hermetic protective cap 4, made of gold-plated KOVAR*, is secured to said substrate with its gold-plate lamination 4-1 in thermal-conduction contact with the stud.

A problem in this respect is that hermetic attachment of the cap is best achieved by "flash" soldering but the solder 5, when melted by heat momentarily applied to shoulder 6, flows along interior gold layer 7 into thermal contact with the stud. As a result, heat is continuously transferred to the chip until the solder has completely cooled. This "long term" transfer of heat may adversely affect the delicate circuits on the chip.

Fig. 2 shows that this problem is avoided if a portion of the interior gold layer 7 is removed leaving an isolated gold pad 7-1 for contact with stud 2.

A process suitable for selective removal of a portion only of the interior gold (thereby preserving the exterior gold for optimal hermetic condition, corrosion protection and thermal transfer) is shown in Fig. 3. The gold area 8 to form pad 7-1 is masked by etch resist 9. Etchant 10 (for instance aqua regia) is poured into the cap to a level below the base gold plate area 11. After etching away the gold between areas 8 and 11, the etchant is spilled off, the part is rinsed, the resist mask 9 is chemically removed and the part is again rinsed. This lea...