Hi Chris, Thanks for your valued suggestion on this. Have a nice day! Best regards, Justin Wu Utilux South China Ltd Phone: +86-755-2850 7521 Fax: +86-755-2850 0927 E-mail Address: [log in to unmask] _____ From: TGAsia [mailto:[log in to unmask]] On Behalf Of [log in to unmask] Sent: Wednesday, April 13, 2011 4:06 PM To: [log in to unmask] Subject: Re: [TGAsia] Solder Ball Hi justin I would like to offer some some comment and suggestions: 1. It is virtually impossible to completely eliminate solder balls with HASL finish since regardless of design, the morphololgy of PCBs is complex and solderballs formed as the PCB passes the air knives generate solder balls as the liquid solder is atomized. It follows that some of these balls will deposit on the surface of holes, between pads and soldermask webs and on the surface. The post cleaning process will remove most, but typically, random balls can be found on close inspection. 2. The best way to eliminate PCB process solderballs is to change the solderable finish to OSP or an immersion finish. Generally this is also benefitial to assembly as well but obviously requires some adjustment of paste/reflow. 3. Assuming you wish to continue using HASL, here are some suggestions to improve the process to minimize the problem: A. You have a choice to completely plug vias with soldermask (best) or to leave them completely open. Tenting vias from one side only or partly filling them will certianly promote the problem as solder balls can be retained in the vias and migrate to the surface later due to handling. These solderballs tend to be larger and a significant concern. B. Soldermask choice can influance retention of small solder balls on the surface. Generally, harder masks are better and UV+thermal cure better than UV cure only. Soldermask suppliers can make specific recommendations for better performing masks engineered for HASL and the good news is these are generally moderate cost. C. The flux used for HASL is very importiant since this provides the barrier to prevent solderballs sticking to surfaces as well as supressing oxidation to ensure copper wetting and leveling. Generally it is a trial and error process to determine the best flux for a given machine but this is a major factor. If flux evaporates too quickly the protective function is lost. D. Solder alloy composition influances wetting, retention on lands and the speed of solidification. The general trend in the HASL working bath is simillar to wave soldering, ie, copper tends to increase and alloy ratios to drift (depends on alloy composition). I consider this a secondary but importiant factor, the smaller the Delta between solidus and liquidus the better. E. Some HASL machines also use an "oil" later in the pot or transition to the air knives to recoat a protective later. Similar case to flux. Post cleaning after HASL is also a major factor. The fluxes used are aqueous and a good line will include: - hot water pre-rinse (>50C) - combined soft brushing and spray rinsing - high presure hot water rinsing with staggered spray bars (to clean the vias) - multiple stage hot DI rinsing - dryer with air knives and hot air Machine needs frequent cleaning and PM to avoid excessive build-up of solids particularly in the front end processes where flux loaded with solderballs must be quickly dissolved. Hot water and suficient time are essential. F. End of line sampling inspection is essential. Since the process produces solderballs it is virtually impossible to achieve zero defects but customer and supplier should agree on a standard of acceptable size and qty in areas of concern. G. Any critial areas such as fine pitch BGA or CSP lands should be a 100% inspection item. However, as long as you use HASL zero solderballs at bare PCB stage is impossible. For criteria you need to consider the PCB technology and risk of solderballs of a certain size or greater causing an electrical fault if they migrate. My personal opinion: elimiate HASL if tpossible, not a zero defect process, you can only mitigate and manage problems. Hope that helps. Regards, C.B. Katzko VP, Research + Development TTM Meadville Asia Pacific Email [log in to unmask] Mobile +86 13817362590 Tel +86 21 37747528 Fax +86 21 37747590 _____ From: WM-FQA-Zhao ZiDe [[log in to unmask]] Sent: 04/13/2011 02:59 PM ZE8 To: <[log in to unmask]> Subject: Re: [TGAsia] Solder Ball Dear Justin Wu: From the photo, we can find the solder ball on topside PTH, due to solder mask in the PTH and caused the hot air chould not through the TH at the HASL process, if void the same question reoccur, the solder mask film need be revised. you can let the PCB manfuacture plant to enlarge the solder mask opening or plug the TH by solder mask. Many Thanks, Best Regards, Zhao Zi De QA Department World Mastery Technology Limited Tel:+86 769 85569149 Ext:862 Fax:+86 769 85262272 Email:[log in to unmask] ----- Original Message ----- From: Justin Wu <mailto:[log in to unmask]> To: [log in to unmask] Sent: Wednesday, April 13, 2011 12:08 PM Subject: Re: [TGAsia] Solder Ball Hi All, We have found some solder balls inside TH on the PCB (See below photo), however there is no exact matching of the defect mentioned in IPC, but according to IPC-A-610 Clause 5.2.7.1, the solder ball is accepted if it is embedded in the solder resist. So, would you please share your experience in such case with me? Thanks in advance! Best regards, Justin Wu Utilux South China Ltd Phone: +86-755-2850 7521 Fax: +86-755-2850 0927 E-mail Address: [log in to unmask] __________ Information from ESET NOD32 Antivirus, version of virus signature database 6037 (20110412) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. 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