Browse Prior Art Database

FLEXIBLE LOW TEMPERATURE ENCAPSULANT

IP.com Disclosure Number: IPCOM000027009D
Original Publication Date: 1994-Dec-31
Included in the Prior Art Database: 2004-Apr-07
Document File: 2 page(s) / 129K

Publishing Venue

Xerox Disclosure Journal

Abstract

Encapsulants presently used to protect wire bonds and other sensitive parts of the thermal ink jet (TIJ) devices require curing at 150°C for about an hour. Once cured, the encapsulant is a very non-yielding and hard solid having a shore durometer in the range of 85-90D. Such a non-compliant solid can severely stress the very delicate wire bonds and may even cause their breakage.

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XEROX DISCLOSURE JOURNAL

FLEXIBLE LOW TEMPERATURE Proposed Classification ENCAPSULANT U.S. C1.346/140R Ram S. Narang Int. C1. GOlD 15/18

Encapsulants presently used to protect wire bonds and other sensitive parts of the thermal ink jet (TIJ) devices require curing at 150°C for about an hour. Once cured, the encapsulant is a very non-yielding and hard solid having a shore durometer in the range of 85-90D. Such a non-compliant solid can severely stress the very delicate wire bonds and may even cause their breakage.

In addition, the sudden introduction of the assembled device at room temperature to an oven at 150°C causes severe stresses in the device due to the relatively large differences in the thermal expansion coefficients of the various elements of the device, e.g., silicon, heat sink, silver-loaded epoxy and the encapsulant. An expected, though undesirable, consequence of these thermally introduced stresses is the cracking of the device at its weakest points, i.e., at the corners of the ink outlets in the channel wafer. Very detailed annealing studies of the system have shown that cracking at the corners of the ink outlets in the channel plate of the TIJ device can be prevented only if the system is not subjected to sudden thermal shock. This requires one of the following to be performed:

1) anneal the system gently by putting the encapsulated device in an oven at an initial temperature no higher than 60°C; raise the temper- ature to 150°C slowly over a period of 30 mins; keep the system at 150°C for an hour; and finally, cool the system down to room temperature over a period of at least 30 minutes,

or

2) find an alternate encapsulant which can be cured at lower temperatures.

XEROX DISCLOSURE JOURNAL - VoI. 19, No. 6 November/December 1994 455

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FLEXIBLE LOW TEMPERATURE ENCAPSULANT(C0nt'd)

It is obvious that the first alternative of slower anneal creates unwelcome delays in the assembly line and is, therefore, not desirable. Under the circumstances, the second choice is to either find or develop an alternate encapsulant which can be cured at temperatures below 100°C in less than an ho...