Film type solder mask evaluation for flip chip BGA

In this paper, the effects of solder mask are studied and two types of solder mask are used in this study, include liquid type and dry film type. Ether liquid type or dry film type solder mask has its own advantage and disadvantage. For liquid type, it is a mature process and can be operated without vacuum environment. However, for dry film type, it needs to be operated in vacuum environment for preventing contamination and void, but dry film type could get better solder mask thickness uniformity and smaller roughness. The test vehicle of this study is 42.5 mm*42.5 mm Flip Chip Ball Grid Array (FCBGA) with 150 um bump pitch composed with different solder mask material. Two kinds of substrate are evaluated in this study: liquid type solder mask (S/M1), dry film type solder mask (S/M2). Substrate roughness, adhesion test, PKG level coplanarity, PKG warpage and reliability test are conducted to evaluate the effect of dry film type and liquid type solder mask on substrate and PKG. The results shows that dry film type solder mask has lower roughness than liquid type. For the part of adhesion test between underfill and solder mask, dry film type solder mask shows similar adhesion strength to liquid type. Shadow moire¿ is employed to measure warpage and the results shows substrate with dry film solder mask has lower warpage. For the reliability life test, two packages are subjected to pre-condition of JEDEC MSL Level 3, TCT1000, HTSL1000 and HAST168, and both two packages passes reliability test.