Phil, As far as holding small dams-we have just recently qualified an LPI from Taiyo that we were repeatedly capable of holding .003in. solder dam. Tony Steinke Circuit Technologies Inc. ----- Original Message ----- From: phil bavaro <[log in to unmask]> To: <[log in to unmask]> Sent: Wednesday, August 01, 2001 12:15 PM Subject: [TN] 0.5 mm pitch components and soldermask relief > We are just starting our development of 0.5 mm pitch BGAs and I am hearing > conflicting reports as to the approach we should take with respect to the > soldermask relief around the solderball pads. > > First of all, the 0.5mm BGA is made up of pairs of pads in a perimeter > layout, along with a larger perimeter also made up of pairs of pads. There > is also a ground block in the center. Basically it looks like two > concentric windowframes with a large gap between the frames for routing. > > Historically we have always made our soldermask 1:1 with the pad size and > then the pwb fabricators would swell the opening so that the soldermask did > not encroach upon the pad and make it a mask defined pad. That works fine > for 1.0 and 1.27 mm pitch devices because there is still enough soldermask > left to actually stick to the board. > > When we reduce the pitch down to 0.5 mm, the gap between and the > registrations swelling, basically eliminates the thicker stripe of > soldermask down to a very thin (and poor yielding) line which may or may > not stick. > > This is the exact same problem we have always had with 0.5 mm QFPs and the > solution was always to permit the pwb fabricator to window out the whole > area between the fine pitch pads. > > So here is the question: > > If we open up the soldermask aperture so that it is something like .065mm > away from the actual etched pad, doesn't that just reduce the producibility > of the board at the pwb house. The reason for specifying this tight > requirement is speculated to be related to reliability but I'm not > convinced yet. > > In reality very few of the pads are strictly etch defined round pads > because many have surface conductors coming off of them which makes the > pads a hybrid of etch and mask defined. The greater the relief of the > soldermask, the more non-uniform the exposed metal pad will become. > > Because there is more surface to wet to, this has the effect of reducing > solderball volume and we expect to see the diameter not the height change > accordingly. > > My suggestion is to eliminate the soldermask wherever the tight pad to pad > areas are so that for two round pads, the aperture would be a very wide > oval shape. This also means that the routing away from the pads has to go > to the outside away from the open soldermasked area. > > The intention here is minimize the enlargement of the pads with respect to > wettable area and at the same time make the soldermask application process > easier. > > Ironically it seems that 0201 pads can also follow this logic. > Hopefully I've explained this in detail enough for everyone to understand. > > What does your land patterns guidelines when it comes to soldermask for > fine pitch QFPs, BGAs, and 0201s? > > All inputs are appreciated. > > Phillip A. Bavaro > QUALCO/\/\/\/\ Incorporated > Engineer, Staff > [log in to unmask] > Pager (858) 271-3640 > Tel (858) 658-2542 Voice mail > Cell (858) 845-9968 (workday) > Cell (619) 602-8644 (offsite, after hours) > Fax (858) 658-1584 > > -------------------------------------------------------------------------- ------- > 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 ---------------------------------------------------------------------------------