Hey Stacy, It sounds as though on paper, your process is OK. Just to fill you in on aspect ratio, that is aperture width/stencil thickness. This is a good rule of thumb for rectangular apertures such as for fine pitch components. For small circular or square apertures most people use the area aspect ratio which is aperture area/wall area. The area aspect ratio should be above 66. Thus on a .005" thick stencil with a .0135" square aperture you are looking at (.0135*.0135)/((.0135*.005)*4) = .675. Actually the area aspect ratio for a .0135" round aperture is the same as that for a square aperture, yet release on the square aperture has generally been proven to be better (don't forget a .002" or .003" radius on the corners). Anyway my point was going to be that I had the exact same apertures ordered on one particular project, and the apertures all clogged up (luckily we caught them at the visual step). It seems the apertures were severely undersized (more like .0122" x .0122"). So are your apertures really 0135"? As Kathy mentioned, kneed or condition your paste. The paste may take a few prints to fully mix and provide the thixotropic characteristics that you want. We use a dummy board for the first print, and then print our first production board. Personally I think you could get away with a .015" aperture if you are dealing with a .0315" pitch product. Even if they undercut your stencil, you should be fine. Good luck.... Steve A > -----Original Message----- > From: My Nguyen [SMTP:[log in to unmask]] > Sent: Tuesday,December 11,2001 11:43 AM > To: [log in to unmask] > Subject: [TN] Inefficient solder on Toshiba micro BGA > > Hello all, > > Problem description: > > Been happening on Rambus - part number tc59rm81xmb. > Ball diametter: 0.5 mm; ball pitch: 0.8 mm, ball > height: 0.4 mm. Pad size: 0.3 mm (11.5 mils) > 5-10% of the time (we run huge amount of them) failure > modules came from opening soder join or no solder join > at all. As we inspect the screen printing process (we > use 5 mils stencil - Dek screenprinting, cleaning > rate: 2 per print, cleaning cycle Wet-Vacuum/Dry), we > found un-event solder deposit. Some pad even has very > little solder or no solder at all. > > Stencil is electro-polish; Diamond shape aperture, > 13.5 mils open used trapezoid shape. > > We afraid that if we open the apperture bigger, then > we may have bridging or solder ball. If we reduce the > stencil to 4 mils to reduce the blockage or > resistance, then we may have in-efficient solder or > many other problem relating thin stencil (damage, > short-life, etc) > > What would be your solution? > > Thanks, > > Stacy > > __________________________________________________ > Do You Yahoo!? > Check out Yahoo! Shopping and Yahoo! Auctions for all of > your unique holiday gifts! Buy at http://shopping.yahoo.com > or bid at http://auctions.yahoo.com > > -------------------------------------------------------------------------- > ------- > 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 > -------------------------------------------------------------------------- > ------- --------------------------------------------------------------------------------- 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 --------------------------------------------------------------------------------- --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------