Reliability development and qualification of a low-cost, PQFP-based MCM

In Motorola´s experience with commercial MCM customers, cost reduction is the largest driving factor for interest in MCMs. Speed and other performance factors are of secondary interest. Development and qualification can add significantly to the total cost of an MCM, so in addition to the normal desire to provide reliable products, the cost of doing so has gained increased importance. Motorola has identified three key factors in providing cost-effective MCMs: leverage single chip package experience, qualify MCM product families (package types), and use only qualified silicon devices in MCM products. This paper describes application of the three key factors to the reliability qualification of the 28 mm MCML Series package, a PQFP- (Plastic Quad Flat Pack) based MCM. An initial reliability evaluation was performed to investigate reliability issues. Subsequent to the results of the initial evaluation, changes were made to assembly processes and materials. The MCM was then submitted to a suite of reliability stresses selected to evaluate mechanical, thermomechanical, moisture and longevity performance. The MCM passed electrical and visual (SAT, or Scanning Acoustic Tomography) reliability requirements for all stresses, and performed well in extended stress tests as well. A procedure is in place to help insure high reliability for subsequent products in the 28 mm PQFP MCM package