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Photosensitive Thermoplastic Solder Dams for Solder Volume Control

IP.com Disclosure Number: IPCOM000081750D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Clark, RJ: AUTHOR [+2]

Abstract

The use of a photosensitive thermoplastic material as a solder dam eliminates a series of process steps including chrome plating and subsequent pad etching, while preventing solder from flowing along the printed-circuit lines of the module which terminate at the chip sites.

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Photosensitive Thermoplastic Solder Dams for Solder Volume Control

The use of a photosensitive thermoplastic material as a solder dam eliminates a series of process steps including chrome plating and subsequent pad etching, while preventing solder from flowing along the printed-circuit lines of the module which terminate at the chip sites.

Such a solder dam is formed on the device by utilizing a thermoplastic material such as AZ1350H* which, when has added thereto 20 grams of ALNOVAL** 429K, results in a phenol-formaldehyde photosensitive thermoplastic material. The material thus is then diluted to a spraying consistency with a suitable thinner. This material is deposited on the lead frame and partially cured by baking in an oven at 85 degrees C for 15 minutes.

Since the described material is a positive working photoresist, the material is then photoprocessed in accordance with standard techniques, to remove the thermoplastic photoresist material from the areas of the lead frame which are to be plated. However, prior to this plating a post-development bake is performed at 130 degrees C and 220 degrees C.

Following this post-development bake, the lead-tin solder is applied to the lead frames and the lead frame is formed and annealed at 300 degrees C. During this lead frame annealing process, the thermoplastic material will stress relieve itself preventing distortion within the lead frame which may be found when more rigid structures, such as polyimide or glass, is...