| To electropolish or not to nickel plate, that is the question. Whether it be nobler in the minds of the competition could be the answer. | I think it will probably depend upon whom you ask the question. If the stencil mfgr. has nichel plating capibility, then you will probably find that nickel plating is the answer. The same for electropolishing. | Something you should keep in mind is that nickel plating is an "additive" process and electropolishing is a "removal" process. So, if you are starting with a cut aperture of 9-mil, after nickel plating you will have something less than 9-mil and visa versa for electropolishing and visa-versa for nickel plating. | When laser-cutting became popular, the chem-etch people said the inner side walls of a laser-etched stencil were not as smooth as chem-etch. So, the laser people had to come up with a way to compensate - electropolish. When the E-Fab nickel stencil was introduced the compensation was to nickel plate a laser-cut stencil in an attempt to stay competitive with the E-Fab. You may have confirmed this logic with your previous experience with the non-plated, non-polished stencil. | Now, lets get to what I think the problem is - aperture contamination. How are you cleaning the stencil? A 20-mil pitch stencil is difficult enough to print through. With 9-mil, you have to take extra care in keeping the apertures clear (rough inner walls or not). Just wiping the stencil will just push paste back into the apertures. I recommend scoping the apertures under high power magnification. I'm willing to bet that you will find solder ball contamination. If solder balls are allowed to stand in the apertures overnight, they will dry like cement and be even more difficult to remove with successive cleanings. Dry paste attracts wet paste and obstructs the apertures resulting in poor paste transfer and poor paste release. | I also recommend and article on our Web Site that was written by a stencil mfgr. "SMT Stencil Cleaning: A Decision That Could Impact Production." (www.smartsonic.com/article.html) You can also find it in the July,1996 issue of EP&P or the August, 1996 issue of Asian Electronics Engineer. | Now, comes the sales pitch. Smart Sonic is the only stencil cleaning process that guarantees to clean any type of solder paste (wet or dry) from any fine-pitch stencil...or your money back! Enough said. | If you have any questions, please call me. | Tel.: 1(800) 906-440-R | Regards, | Bill Schreiber | | Hi all, | | We are currently having problems with a laser-cut stencil that is | | electropolished and nickel plated with 9-mil openings. The paste does | | not release well from the apertures. We are having to wipe after every | | print. The board is fixtured well and we have been using the same | | paste for the last two years. We had a different laser-cut stencil in | | production from a different manufacturer with the same 9-mil opening, | | but this stencil was not electropolised or nickel-plated. With this | | stencil, the paste release was excellent and we never had to worry | | about wiping. | | Does anyone have any input into whether or not laser-cut stencils | | should be electropolished and nickel plated? I have heard | | contradicting opinions on this subject. One source has said that you | | do not want to electropolish laser-cut stencils because the | | rough laser walls will give you a better paste release. Whereas, | | another source has said that the smooth laser walls will give you a | | better paste release. | | Also, what benefit does nickel plating give you? Does the paste tend | | to roll better with nickel plating? Do you tend to get more or less | | paste deposit on the boards with nickel plating? Does it increase the | | life of the stencil? | | Has anyone using laser stencils seen major differences between | | the quality of different stencil manufacturers? | | Any input into this subject would be greatly appreciated. | | Thanks, | | Todd
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