Was this perhaps a sales presentation?

I have to question any presentation that tries to suggest that lead bearing pastes do not pull back to the pad during reflow.

I might accept the statement that the unleaded pastes pull back just as well, but paste-in-hole technology with lead bearing pastes is proof that Sn63Pb37 does not "just sit there".

I am more concerned with the way that the unleaded pastes outgass and subsequently wet to the pad when printed in a striped pattern as opposed to the lead bearing pastes.

I have seen first hand (and not resolved yet) that lead free pastes form huge voids beneath a device with a large center slug (5 mm square) such as a 116 pin BCC++ package.

Phil



MA/NY DDave <[log in to unmask]> wrote:
Hi IPC LF Listservers,

I just saw a presentation on some work about print mis-positioning with
many different SAC305 LF pastes compared to a SnPb paste control.at

As part of the conclusions SnPb preformed not as good as LF. As the print
became more off the pad (.003, .006inches etc), the SnPb control just sat
there on top of the solder mask while the LF pulled back to cover nicely
the PCB land. This doesn't seem right to me unless there was something off
with the SnPb control.

So have any of you seen this effect??
What are your thoughts??

Yours in Engineering, Dave
YiEngr, MA/NY DDave

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