Hi, John,

Welcome to TN. I have to answer your question with more questions, like:

1) Are the problem components used anywhere else on the board and are they
  being properly wetted in those other positions?
2) What board finish are you using?
3) What is the termination finish of the components? Do they have any
  silver content for any reason?
4) How old are the components and what conditions have they been stored
  under?
5) Are the same locations failing to wet each time, or are some wetting in
  some cases and others in others?
6) What solder are you using?

I suspect you have an oxidisation problem with the component leads, perhaps
leeching of silver if there is any silver content. If it's a silver
problem, try using a 2% silver solder to redress the balance. If it's
oxide, you will have to replace the components or re-tin them in a solder
pot with a very aggressive flux.

Maybe I can help more with more detail.

Peter Duncan





                    John Brown
                    <johnbrown118@HO        To:     [log in to unmask]
                    TMAIL.COM>              cc:     (bcc: DUNCAN Peter/Asst Prin Engr/ST
                    Sent by: TechNet        Aero/ST Group)
                    <[log in to unmask]        Subject:     [TN] Non-wetting
                    >


                    11/21/01 04:54
                    PM
                    Please respond
                    to "TechNet
                    E-Mail Forum."






Good Morning, this is my first posting to this forum I hope to get some
help. We are building a small PWB with 4 per panel. The problems we are
encountering are on 0603 resistors & capacitors and SOIC (8pin) etc. These
are all located near to or the center of the PWB. There is paste on the pad
and the component placed properly but the paste will not wet onto the leads
or terminations.
What have we done?
1. Run the PWB at various profiles even the highest. Still have problem.
2. Changed from no clean to aqueous with an agressive flux. Still have
problem.
3. Changed screen apertures. Still have problem.
This PWB is multi layer and heavily populated.
Are there any hints as to what we do next?

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