Study of self-alignment of μBGA packages

Author

Hung, K.C. ; Chan, Y.C. ; Tu, P.L. ; Ong, H.C. ; Webb, D.P. ; Lai, J.K.L.

Author_Institution

Dept. of Electron. Eng, City Univ. of Hong Kong, Kowloon, China

Volume

23

Issue

4

fYear

2000

fDate

11/1/2000 12:00:00 AM

Firstpage

631

Lastpage

636

Abstract

In this paper, a detailed study of the self-alignment of μBGA packages is presented. Complete self-alignment can be achieved even for a misalignment of the package of larger than 50% off the test board pad centres. A small residual displacement of the package from perfect alignment after reflow is observed. The reason for this displacement is the action of gas flow viscous drag on the package during reflow. The use of eutectic SnPb solder paste slightly reduces self-aligning ability, due to the increase in the solder volume, which reduces the restoring force. Exposure of the solder paste to a 25°C and 85% RH humidity environment also has a detrimental effect on the self-alignment of the μBGA package, due to solvent evaporation and moisture absorption in the paste causing solderability degradation. The self-alignment of the package is also affected when there is slow spreading of molten solder on the pad surface. This is attributed to the reduction of restoring force due to the decrease in effective wetting surface area of the board pad.

Keywords

ball grid arrays; chip scale packaging; humidity; reflow soldering; μBGA packages; 25 degC; effective wetting surface area; gas flow viscous drag; humidity; moisture absorption; molten solder; residual displacement; restoring force; self-alignment; solder volume; solderability degradation; solvent evaporation; test board pad centres; Automatic testing; Bonding; Chip scale packaging; Circuits; Consumer electronics; Drag; Electronics packaging; Fluid flow; Humidity; Lead;

fLanguage

English

Journal_Title

Advanced Packaging, IEEE Transactions on

Publisher

ieee

ISSN

1521-3323

Type

jour

DOI

10.1109/6040.883752

Filename

883752