I realize that minimal gold (3-5 millionths) is best for soldering, but: a. Isn't that a pretty tight range? b. What if there is something on the other side, say, that will be used for wire bonding? MB ______________________________ Reply Separator _________________________________ Subject: RE: BGA FInish Author: [log in to unmask] at SMTPLINK-HADCO Date: 5/7/96 02:24 PM Hi Gita, Q: What is the preferred surface finish for PWB's with PBGA packages? A: The critical process factors for BGA assembly are: * Surface Coplanarity * Solder Volume * Solderability * Moisture Sensitive (PBGA) It 's okay to use Entek 106A, but you should consider the solderability of second reflow or BGA repair if there is any. Gold is very solderable, and just as important, very coplanar. It is increasingly becoming a popular choice for SMD fine pitch board assemblies. With gold, there is no embrittlement concern as long as the thickness of gold is 0.000003-5". You can consider gold as an alternative to HASL. Q: Using Entek boards, what kind of flux is better to use, NO CLEAN or water soluble? A: No clean Flux is definitely a better choice. According some technical studies I read, water soluble is more likely to form solder balls if the temperature profile and solder mask design are not optimum. In your case, finding solder balls beneath the BGA is the last thing you want to see. With no clean flux, the reduction in solid content will tightens the process window and nitrogen atmosphere reflow has proven helpful in improving process yield when no clean flux is being used. Thanks [log in to unmask] ---------- From: TechNet-request To: TechNet Subject: FAB/ASSY: PREFERED PWB SURFACE FINISH FOR BGA Date: Monday, May 06, 1996 2:08PM What is the preferred surface finish for PWB's with PBGA packages? I have been looking at some published industry data regarding PWA assemblies with plastic BGA's and so far all have had HASL surface finish and very little data on OSP (organic Solderability Preservatives such as Entek) coated boards. Has anyone had any OSP coated (Entek 106) mother board designs with BGA packages in production? What are the pro and con's with HASL Vs. ENTEK for BGA assembly? Using Entek boards, what kind of flux is better to use, NO CLEAN or water soluble? The preferred surface finish for assembling fine pitch components has become Entek (or Entek equivalent) for better coplanarity criteria, but is there a danger using Entek boards for BGA assembly? I would greatly appreciate any information you can share with me. [log in to unmask] (800) 289-3355 EXT 85408 or 512-728-5408 direct line Thanks, Gita