White tin immersion finish

We are investigating alternatives to HASL finishes for more dense PWBs. OSP is not a good choice because of low solid flux and possibly long shelf life. Immersion gold is expensive and so far has been more difficult to wave solder. Has anyone had experience with a "White Tin" process? What material is "white tin". Can it be used interchangeably with HASL PWBs? Any help would be appreciated. David

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| We are investigating alternatives to HASL finishes for more dense PWBs. OSP is not a good choice because of low solid flux and possibly long shelf life. Immersion gold is expensive and so far has been more difficult to wave solder. Has anyone had experience with a "White Tin" process? What material is "white tin". Can it be used interchangeably with HASL PWBs? Any help would be appreciated. | David David: It is a solderability perservative, like OSP. Ckeck the site below. Dave F

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We have mixed to negative feelings about Omikron, but I beileve it is due to problems with the board fabricator rather than the process itself. When done properly, our Omikron boards have had very good solderability. However, we have had several runs that had major solderability problems. Apparently, the tin deposit was too thin, and the boards could not hold up to multiple heat cycles. I don't know if this is a tricky process or not, but our current board house can't seem to get it right. Consequently, we are about to try out a different board house as well as a different process (immersion silver).

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| We have mixed to negative feelings about Omikron, but I beileve it is due to problems with the board fabricator rather than the process itself. When done properly, our Omikron boards have had very good solderability. However, we have had several runs that had major solderability problems. Apparently, the tin deposit was too thin, and the boards could not hold up to multiple heat cycles. | I don't know if this is a tricky process or not, but our current board house can't seem to get it right. Consequently, we are about to try out a different board house as well as a different process (immersion silver). Gentlemen, I have been investigating all this for over three years. As I have said before, very emphatically, I want a way out of HASL. I have used every other finish known to industry and really believed immersion gold over immersion nickel to be the answer. In light of recent findings, by some of the big device suppliers, I am now searching for answer to my hoped for answer in gold. You might check out the latest rounds on this subject on the IPC Tech Net. It's getting exciting. I've tried silver. With a well managed immersion process, it works well. Silver migration problems are no longer an issues in such small amounts. However, shelf life is still an issue. I don't know how long shelf life may be, but I have noticed the typical silver oxide (tarnish) build over time on some sample bare boards. This is a very serious issue, and I wish us all well. Earl Moon

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