At 09:06 AM 2/5/2008, Ryan Grant wrote: >Thanks John. I'm not too worried about laser vias because they have a >bottom. If one doesn't pre-fill the via like you mention, a solder void >will occur with BGA's. However, the void is usually small. Although, >I'll have to see what the relative void size is on a 0.8mm pitch CSP... Depending on uVia quality and aspect ratio it can be a problem even at .8mm. If the uVia is too rough or narrow at the top it won't wet out and the expanding gas has to go somewhere -- usually late in the cycle when combined gas law is working to create a very large bubble in the solder ball. I've seen large enough voids in solder ball from poor uVia quality or uVias with overhanging/thick copper at the knee that it caused adjacent balls to bridge. I've got some pictures archived l and could post them if you're interested. dw >What about through vias that are not filled with epoxy? Have you >soldered on top of those? > >-----Original Message----- >From: John Burke [mailto:[log in to unmask]] >Sent: Tuesday, February 05, 2008 10:00 AM >To: 'TechNet E-Mail Forum'; rgrant >Subject: RE: [TN] Open via in pad - any success? > >When I did that on a single sided via (laser drilled) I pre-filled the >vias >with a separate stencil/reflow operation to "level the field" followed >by >water cleaning followed by regular assembly techniques > > > >John Burke > >(408) 515 4992 > >-----Original Message----- >From: TechNet [mailto:[log in to unmask]] On Behalf Of Ryan Grant >Sent: Tuesday, February 05, 2008 8:38 AM >To: [log in to unmask] >Subject: Re: [TN] Open via in pad - any success? > >Thanks Paul, > >If you and two others can do it, I guess it can be done... I'm glad I >asked before I made a fool out of myself. > >So now the question is, how did you do it (if you can tell me)? > >Whenever I've tried it, either gravity would cause the solder to sag out >the bottom, or the via would suck solder away from the joint. > >Thanks, >Ryan > >________________________________ > >From: Paul Edwards [mailto:[log in to unmask]] >Sent: Monday, February 04, 2008 6:43 PM >To: TechNet E-Mail Forum; rgrant >Subject: RE: Open via in pad - any success? > > >Ryan, > >It really depends on the size and depth of the via, the via to pad >diameter ratio.... > >Q: has anyone been successful with a via in pad that is not plugged?.. >A: YES, both through and blind vias > >Q: If so, was it double sided? >A: YES if you mean a double sided PCB, and YES if you mean it was a >through via.. > >Q: ...was one side connected to a BGA ball? >A: YES > >Paul > >-----Original Message----- >From: TechNet [mailto:[log in to unmask]] On Behalf Of Ryan Grant >Sent: Monday, February 04, 2008 4:55 PM >To: [log in to unmask] >Subject: [TN] Open via in pad - any success? > >Hi All, > >I just got told by a design engineer that LaserJet printers are built >using via in pad where the via is NOT plugged. He claims the via is >filled with solder first, then goes through the normal SMT process. > >He intends to use this to connect a BGA ball on one side of the board to >a cap on the other side using an mechanically drill via that is not >plugged. > >Before I call BS on this, and tell him "do not pass go until that via is >plugged, flattened and plated over", has anyone been successful with a >via in pad that is not plugged? >If so, was it double sided? >And, was one side connected to a BGA ball? > >Thanks, >Ryan > >--------------------------------------------------- >Technet Mail List provided as a service by IPC using LISTSERV 15.0 >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 or (re-start) delivery of Technet send e-mail to >[log in to unmask]: SET Technet NOMAIL or (MAIL) >To receive ONE mailing per day of all the posts: send e-mail to >[log in to unmask]: SET Technet Digest >Search the archives of previous posts at: >http://listserv.ipc.org/archives >Please visit IPC web site >http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional >information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 >ext.2815 >----------------------------------------------------- > > >________________________________ > >This email and any attachments thereto may contain private, >confidential, and privileged material for the sole use of the intended >recipient. 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