Soldering to Immersion Tin surface finish

Can anyone shed some light on this for me ? Subject: Soldering to Immersion Tin surface finish I am looking for info. (pro and con) and/or 1st hand knowledge processing PCB's with Immersion Tin finish through SMT and Wave. Do profiles need to be different? Solderpaste considerations? Anything else?

In the past I have experienced selective non-wetting of the solder to the immersion tin surface and am starting to see more of this surface finish on boards.

reply »

First, consider checking the fine SMTnet Archives. Look for threads on "white tin", in addition to "immersion tin". We�ve had a cuppla good ones of late. Merix [http://www.merix.com] gives a good comparison of different solderability preservatives. Dexter and Florida Cirtech [http://www.floridacirtech.com] are the two process suppliers in the US.

"Do profiles need to be different?" � No

"Solder paste considerations?" � None

"In the past I have experienced selective non-wetting of the solder to the immersion tin surface and am starting to see more of this surface finish on boards." � We see this also. Most often this is related to board fab. When thinking about your fab, consider �

2 Have your supplier apply the white tin at the end of the process. If the tin is applied BEFORE silk screen cure, the cure process can artificially cause a dry-age acceleration, promoting intermetalic growth before you even get the product. 3 Most common reason for solderability issues with the white tin surface coating during multiple thermal excursions is a low white tin deposit. In almost every case we've seen, when the first pass or second side solders fine and then problems arise, the cause is insufficient thickness of white tin that was on the board. 4 Immersion white tin with a minimum thickness of 0.65 microns with a maximum thickness of 1.5 microns.

reply »