Steve, When you say that the "re-used" solder paste will not perform like it is advertised to, do you basically mean that the solder defect rate will go up, or reliability will go down? Specifically, what would be the down side of re-using solder paste? Could the paste not be scraped off of one stencil and placed on a stencil for the next build? It seems like it could, especially since most stencil paste manufacturers are quoting >8 hour stencil life. We "re-use" solder paste when changing out the screens for UP TO 4 days, and I'm not convinced that we are doing the right thing. We use a no-clean paste and our environmental conditions inside the plant change considerably from season to season, for example, the winter humidity/temperature is around 15%RH/75 F, however, in summer it's around 65-75%RH/65-80 F. This is the down side of living in the desert with evaporative cooling and forced air heating. I am relatively new at my company, but what I have seen so far is a significant occurrence of mid-chip solder beads in the summer, and an almost nonexistent occurrence in the winter. The solder bead problem occurs whether the paste is from the "re-use" jar or fresh out of the tube. Other than solder beads, the post-reflow defect rate is <500 PPM (suspect the main contributors are part/design related). Since I'm a new kid in SMT, I appreciate all of the excellent advice from everyone in TechNet! Thanks. Howard Watson SMT Mfg. Eng. AMETEK/Dixson "Stephen R. Gregory" <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 02/15/01 08:22 PM Please respond to "TechNet E-Mail Forum."; Please respond to SteveZeva To: [log in to unmask] cc: Subject: Re: [TN] Solder paste reuse In a message dated 2/15/2001 8:46:23 PM Central Standard Time, [log in to unmask] writes: << Solder paste reuse: does anybody has this practice? Obviously, my solder paste supplier does not recommend it. Nicolas Ortiz Process Engineering Group Leader Conexant Systems >> Hi Nicolas, Your supplier is not recommending it to in order to sell you more paste, it is a valid recommendation. I'm not quite sure about what you mean by "reuse", but if you mean taking paste off a stencil, putting it back in a jar after a run, and then keep using it, that's a bad idea. The paste will absorb moisture, the volatiles in the paste will evaporate, basically changing everything about the formulation of the paste = not performing like it's been advertised to do...I don't know of any manufacturer of solder pastes that would recommend to reuse solder paste after it's been dispensed on a stencil... I do however, understand your concern about the expense when throwing away solder paste...it's not cheap, anywhere from $50.00-75.00 for a 700-gram jar. But you can recover some of the costs through recycling...Alpha/Fry Metals will recycle solder paste and give you back the money that the tin/lead market prices are at the time you turn it in... Bottom-line, don't "reuse" your solder paste...it'll bite you... -Steve Gregory- --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------