my experience is the same as John's on this issue i.e. do open it up we once shipped a board to fab and forgot to do this they called us up and advised that we do and used a descriptive term (opening up the mask) which i can't recollect
it wasn't 'block' but i can't recall it, something like 'moat' or 'bar'? any one know the common term ? Dennis Saputelli "John A. Ross [RSDTV]" wrote: > > > -----Original Message----- > > From: Tom Robinson [mailto:[EMAIL PROTECTED] > > Sent: Tuesday, December 16, 2003 9:26 PM > > To: Protel EDA Forum > > Subject: [PEDA] Solder mask... > > > > > > Is it ok to block open the solder mask on gull-wing i.c.'s with .4mm > > AND .5mm pitches? > > > > It seems to get enough web in between the pads to stick will cause a > > LPI registration thats too tight, with possible smearing. And if you > > make the pads themselves too narrow -- thats another problem. > > Tom > > I always block open the pads on these pitches. > > It is not so easy to get a manufacturer to get SM registration right at > these tolerances although it is possible. > > Most quick turn boards I have had to take as 'free issue' parts to assemble, > which have not blocked off these areas, I have had quality issues with the > finished joints around these fine pitch pads. > > I have never had an issue with blocking them open, biggest solder mask issue > I have ever had was when the SM thickness to finished pad height > differential was too much (SM height was bigger than finished pad by a lot) > and we had gasketing issues from the paste screen to the pad, causing > problems like, paste bleeding out on the PCB side of the screen, some > shorts, failed 3d inspection after print cycle, loose solder ball symptoms > and aperture blockages, with our MPM printer having to make undue clean > cycles between prints. Also undue print down force had to be applied to > squeegee blades, increasing wear and decreasing accuracy. > > Never had solder ball or short issues as long as the board is printed > correctly and the oven specifically profiled to suit your board. (also > optimise paste volumee, height, reductions...) > > John -- _______________________________________________________________________ Integrated Controls, Inc. Tel: 415-647-0480 EXT 107 2851 21st Street Fax: 415-647-3003 San Francisco, CA 94110 www.integratedcontrolsinc.com * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:[EMAIL PROTECTED] * * To leave this list visit: * http://www.techservinc.com/protelusers/leave.html * * Contact the list manager: * mailto:[EMAIL PROTECTED] * * Forum Guidelines Rules: * http://www.techservinc.com/protelusers/forumrules.html * * Browse or Search previous postings: * http://www.mail-archive.com/[EMAIL PROTECTED] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
