Hi, You did not say what the thickness difference was that you are seeing. By the description of 'mounded" I will assume, that we are talking thickness in the 1 mil (1000 microinch) range. HAL is capable of producing Thickness' on QFP sites that are well within any assembly uniformity (coplanarity) requirements that I am aware of for 20 and 25-mil pitch QFPs. There is no industry standard that I am aware of on HAL thickness and all HAL is often considered equal. This creates many issues when we discuss capability. Two common specifications called out are 80-800 microinches and 100 - 1000 (or 100 - 1500) microinches. I have been processing PWBs to the 80 - 800 specifications for 15 years and have never had a reject for solderability or coplanarity on QFPs. We typically hold a mean around 300 microinches with a standard deviation of around 50 on QFP sites. Having said that, thickness control will be dependent on the HAL process that they were run on. Not all HAL is equal. Vertical HAL typically has a much higher difference in the pad height than horizontal HAL for QFP sites. It is very important to process panels at an angle to achieve uniformity. All HAL processes are not capable of this. This is not needed for some technologies, but as you get into QFP surface mount features, it becomes critical. A paper called " Benefits of Angle" is downloadable in the tech library at www.huggroup.org . A HAL Specification Guideline is downloadable at www.tet-halco.com. I hope this helps. If I can be of further assistance please feel free to contact me off line for details of studies and related questions. Sherry Goodell Mgr. Applications Engineering TET Halco, 8 Delta Drive, Londonderry, NH 03053 Phone: (603) 437-8653 Fax: (603) 434-4156 ----- Original Message ----- From: Hamilton, Richard CLE 4454 <[log in to unmask]> To: <[log in to unmask]> Sent: Wednesday, August 09, 2000 4:52 PM Subject: [TN] QFP Pad Height Uniformity > 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. > 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 ##############################################################