There is no doubt in my experience that gold immersion is the surface coating of choice for SMT designs where flatness is a primary concern. HASL has shown various drawbacks from one supplier to another in terms of flatness adherence and OSP handling is problematic at assembly and forget about rework. White immersion is only as good as the pcb fabricator applying it. My question is this, with the de-lead drive in Europe now taking hold, what performance effects will take place in soldering. Are there any new products out now that respond to this move to take "Sn" out of the system? Charlie McMahon -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Brooks Bill Sent: Friday, August 11, 2000 11:55 AM To: [log in to unmask] Subject: Re: [TN] QFP Pad Height Uniformity I find this thread interesting.... In the 70's we made boards and our customers complained of not getting 'enough' solder after going through the Hydro-squeegee process for leveling the solder... Of course the method was more crude... we dipped the boards into molten solder and ran them through a hot fusing oil and sprayed the surfaces of the board with the hot oil to remove excess solder... it's similar to the hot air leveling but with more smoke... the oil has nasty smoke that it releases when sprayed at high velocity... I guess that the oil was more efficient in the solder removal process than the hot air is... no? I guess Hydro-squeegee technology wouldn't be acceptable to the EPA? But it would make a very flat solderable surface. White Tin isn't a panacea either... Ni/AU has it's problems... Gold is expensive... what's a board manufacturer to do? Bill Brooks Senior PCB Designer - [log in to unmask] Zoneworx, Inc. 40925 County Center Drive, STE 200 Temecula, CA 92591 http://www.zoneworx.com Tel: (909) 296-1226 x 1037 Co-Director / Education Officer / Webmaster for the San Diego Chapter of the IPC Designers Council http://www.ipc.org/SanDiego/index.html -----Original Message----- From: Clive ffitch [mailto:[log in to unmask]] Sent: Friday, August 11, 2000 12:56 AM To: [log in to unmask] Subject: Re: [TN] QFP Pad Height Uniformity Richard, May not be an immediate solution for you, but a change to Ni/Au finish at minimal (if any) cost penalty could provide a better way forward. We spec Ni/Au in preference to HASL for anything with 25thou pitch or smaller for the very reason/problem you state. HASL cannot give us the level finish we need for fine pitch SMT. Hope helps, Clive ffitch MBUK Stevenage, England -----Original Message----- From: TechNet [mailto:[log in to unmask]] Sent: 10 August 2000 00:55 To: [log in to unmask] Cc: [log in to unmask] Subject: [TN] QFP Pad Height Uniformity *** WARNING *** This mail has originated outside your organization, either from an external partner or the Global Internet. Keep this in mind if you answer this message. Hello all, I hope I can relate what is happening here so all of you experts can lead me down a path! (Am I asking for it or what?) 25mil and 20 mil QFP's on a double sided PWB. We are seeing variances in the total height of the pad and resulting HASL finish. Specifically maybe 5-10 pads out of the 84 on the QFP exhibit an increase in HASL result in that the solder is mounded on top of the copper. The rest of the pads all are flat in nature with good HASL finish observed. We are being told that the resultant solder height is not controllable. Is this true? Is it unexpected to see all 84 pads looking the same? The situation came to light at the post printing process where a visual inspection detected abnormal paste placement. We ended up with either more solder per pad (potential shorts) or less solder than normal (potential reduced reflow) per pad. When I queried TechNet some time ago about stencil aperture sizes, the bulk of the results came back that apertures were ordered at some percent smaller than the actual pad size. In the neighborhood of 5-20% reduction. If apertures are smaller than the pad size wont this add to problems of uneven pad heights, assuming pad heights are not very well controlled? As usual, Thanks in advance. Richard Hamilton Clemar Mfg. / Rain Bird [log in to unmask] ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. 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If you need assistance - contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ############################################################## ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ##############################################################