焊球阵列封装(BGA)中吸水性测量概述

Survey of Measurement of Water Absorption in BGA

塑料焊球阵列封装(PBGA)对爆米花裂纹的抵抗力较小,一旦因焊接产生的高温使水汽迅速地扩展,就会发生此种现象。在粘片胶处发生爆米花现象,因此,必须研究在粘片胶附近发生的吸水性和解吸现象。本文主要讨论BGA中爆米花裂纹产生的机理,特别是对吸水性分布情况的探讨。用重水进行模拟分析,因为重水与水的吸收性比较接近。采用飞行时间次级离子质谱分析法(TOF-SIMS)来测量重水吸收性分布。弄清BGA封装主要是通过模塑包封部分的上部吸收水分的,由基板吸收的水分是少量的。因BGA基板具有叠层结构,水分不能首先透过基板。应优化BGA封装系统的设计,使其不易产生爆米花裂纹。

The PBGA ( Plastic Ball Grid Array ) package has poor resistance to popcorn cracking, which occurs when high temperatures involved in soldering cause water vapor to expand rapidly.Popcorn cracking occurs at die attach paste and therefore water absorption and desorption occurring in the vicinity of die attach paste must be studied.The mechanism of popcorn cracking in a BGA, particularly from the aspect of water absorption has been examined in this article. Water absorption was simulated by use of deuterium oxide. Deuterium oxide absorption distribution was measured by time of flight secondary ion mass spectroscopy (ToF-SIMS ).The conclusions are following: The water is absorbed mainly through the upper side of molded portion of the BGA package, and that absorption through the substrate is small.A BGA substrate has a laminated structure, and therefore water cannot penetrate the substrate first.