Browse Prior Art Database

Surface Solder Mounting Pad Geometry

IP.com Disclosure Number: IPCOM000038667D
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 1 page(s) / 13K

Publishing Venue

IBM

Related People

Hebert, TM: AUTHOR [+3]

Abstract

A surface solder attachment technique is described for attaching electronic modules to circuit cards. Surface solder devices are required to withstand many of the environmental conditions expected of the more traditional leaded (pin- in-hole (PIH)) technologies. One of the more severe conditions, to which assembled printed circuit cards are submitted, is the twisting or torque test. This test is designed to simulate the typical deflections that the card will see in actual use as it is plugged into its higher level package (mother board) or as other cards are plugged into it (daughter cards). As force is applied to the assembled card, it tends to deflect.

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Surface Solder Mounting Pad Geometry

A surface solder attachment technique is described for attaching electronic modules to circuit cards. Surface solder devices are required to withstand many of the environmental conditions expected of the more traditional leaded (pin- in- hole (PIH)) technologies. One of the more severe conditions, to which assembled printed circuit cards are submitted, is the twisting or torque test. This test is designed to simulate the typical deflections that the card will see in actual use as it is plugged into its higher level package (mother board) or as other cards are plugged into it (daughter cards). As force is applied to the assembled card, it tends to deflect. Since the components which are mounted on the card are very rigid (either thick plastic modules or ceramic-based modules), the components do not give and a stress is generated at the joints where the modules are soldered onto the printed circuit card at the module leads. The only material present to withstand this stress is the solder which forms the electrical and mechanical joints. Should the stress at these joints become too great, the solder joint cracks and the joint may fail both electrically and mechanically, causing the card assembly to fail. With standard PIH technology, the leads of the modules are inserted through the card and then the pin is soldered to the circuitry using the hole as the contact area. The card material and the pin flexibility essentially establish the solder joint strength, and these parameters may be varied to optimize the resistance to deflection. Surface solder devices do not have pins that protrude through the card and the strength of the solder joint is determined by the solder volume and the geometry of the mounting pad. The optimal solder joint strength is obtained when the module lead is placed 100% on the mounting pad. The vast majority of the l...