John, Enjoyed your tent/plug dissertation (I know, I gotta get out more). I'm just wondering about the need to do either. Why not leave them open, or let them fill during wave solder? Ralph Vaughan Boeing-atlanta > ---------- > From: John Waite[SMTP:[log in to unmask]] > Reply To: TechNet E-Mail Forum.;John Waite > Sent: Thursday, April 23, 1998 1:16 PM > To: [log in to unmask] > Subject: Re: [TN] Plugging via holes > > HI Joe, > There are many techniques being used for via hole > plugging/tenting. > First, Tenting is a "covering" of the hole with a material > (typically a D/F type), and > plugging is the attempt to "fill" the hole completely. We need to > distinguish between the two > due to acceptability and application techniques. > tenting is easy: The soldermask artwork is void of any clearances > for the Via holes and by > way of process, the d/f is exposed/polymerized and stays in place > during the developing phase. I > have also used a "high conformance soldermask material" (no names > implied) in conjunction with > LPI for some applications. I would not recommend this as a primary > alternative by any means. > Plugging is typically performed by a screen/stenciling operation. > Many people are using a > thermal cure soldermask, but I have had very good success with a UV > material that has been > designed for via plugging. (the pigmentation is lower, allowing for > better UV energy exposure to > the center of the plug). I also like the use of these types of "via > plug" materials due to the > solids percent. Most thermal masks are approx. 70-80% solids and UV's > are close to 100% solids, > thus less shrinkage of the plug during curing. > The next issue is to plug before or after lpi, before or after > soldercoat. I liked to plug > before LPI. In doing so, We laid down a better profile for the lpi to > cover, and minimized the > amount of lpi pulled up during exposure from the via area due to the > thickness of the LPI versus > exposure energy at the hole. This situation was due to a screen > printing process (flooding of > the hole) and was minimized when we incorporated an alternate > application process (in our case, > spraying of the lpi). By applying prior to LPI, we also cleared up > any aesthetic concerns our > customer had due to the different color "dots". Before implementing > this, prove out your > preclean process. I won't bore you with details unless you ask this > (long subject). > Some people will apply after soldercoating due to the theory that > the copper should be > covered with solder and any skips or missed plugs will not be as > detrimental. Also another long > subject of debate. My personal thoughts (as small as they may be) are > that It is even more > difficult to clean a hole after soldercoating since it is smaller and > has a greater potential of > flux residue to be entrapped. > In any event, however you decide to plug/tent. The following are > critical areas to check: > 1) insure that any tin (or tin/lead) residue is removed during the > stripping stage. I would > recommend that tin be used as an etch resist, since it is easier and > more environmentally > friendly to strip than tin/lead. > 2) profile your preclean. Different methods may create issues, > dependent upon when and how > you plug. > 3) run some tests with different size vias to find you limitations > for stripping, cleaning > and plugging. If you're plating the hole down to .008", then plugging > could become a Moot point. > > 4) Get data from your customers as to how they like the plug > process to be done. I've had > accounts that insist on double sided via plugging. This is extremely > difficult with thermal > masks due to the outgassing that will occur on side 2 of the plug and > the "volcanoes" remaining. > this could interfere with cleaning/assembly operations. I have had > some pretty good success with > 2 sided via plugging of UV materials, but am not saying that this is a > proven industry process. > I guess I could give some more concerns/ideas/comments, but I'm > sure that our peers also have > some success/failure stories to share. If you would like any more of > my long winded > comments/ideas, Email me direct and we can discuss off-line where I > can mention some material > types. Good luck. JOHN WAITE > > Hurst, Joe wrote: > > > Hello Persons: > > > > Any common ways of tenting and plugging standard via holes > > (0.016) ? > > > > Thx > > > > Joe H. > > > > ################################################################ > > TechNet E-Mail Forum 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://jefry.ipc.org/forum.htm) for > additional information. > > For the technical support contact Dmitriy Sklyar at [log in to unmask] > or 847-509-9700 ext.311 > > ################################################################ > > ################################################################ > TechNet E-Mail Forum 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://jefry.ipc.org/forum.htm) for > additional information. > For the technical support contact Dmitriy Sklyar at [log in to unmask] or > 847-509-9700 ext.311 > ################################################################ > ################################################################ TechNet E-Mail Forum 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://jefry.ipc.org/forum.htm) for additional information. 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