Journal of SMT Article

Sensitivity of Copper Dissolution to the Flow Behavior of Molten Sn-Pb Solder

Authors: P. T. Vianco, J. A. Rejent, A. C. Kilgo, and S. E. Garrett
Company: Sandia National Laboratories
Date Published: 6/1/2015   Volume: 28-2

Abstract: As printed circuit board (PCB) feature sizes continue to become smaller, it is critical to understand the details of the Cu dissolution process that accompanies the use of solder fountain and wave processes. In response to an application in which surface mount pads experienced unexpected dissolution by the outflow of molten tin-lead (Sn-Pb) alloy from a solder fountain, a study was initiated to examine the spatial characteristics of Cu dissolution caused by flowing Sn-Pb solder at 271°C. Initial trials with Cu coupons yielded a dissolution rate of 0.54 ± 0.33 microns/s. But, the data displayed too much scatter to fully capture important spatial effects. Therefore, PCB test vehicles having a Cu pad pattern were exposed to flowing solder for 20, 60, or 90 s. The data indicated that dissolution occurred on two length scales: (a) a large scale comparable to that of the solder fountain and (b) a small scale similar to the size of each Cu pad. The dissolution rate was separated into two values based on pad location relative to the stagnation point:

Inner pads (near to the stagnation point): 0.31 ± 0.04 microns/s

Outer pads (distant from the stagnation point: 0.53 ± 0.04 microns/s

There were no indications of pad lifting. The appearance of the remnant solder film did not provide an indication of the degree of Cu pad loss underneath it, including any dewetting caused by the local loss of entire pad thickness. This study provides important insight into the dissolution behavior of flowing molten solder as a critical consideration towards the development of a successful assembly process.

Keywords: 

Copper dissolution, molten solder, fluid flow



Cost to download:

  Members: Free! (Log on to receive the member rate)
  Non-Members: $10

Why become an SMTA member?

Not a member yet? Join SMTA today!

Notice: Sharing of articles is prohibited. Downloaded papers must only be stored on a local hard drive and not in a shared repository either internal or external.


Back


SMTA Headquarters
6600 City West Parkway, Suite 300
Eden Prairie, MN 55344

Phone 952.920.7682
Fax 952.926.1819
Home
Site Map
Update Your Info
Related Links
Send Us Feedback
Contact Us
Privacy Policy
↑ Top