Immersion gold by its nature will be influenced by the circuit pattern. Large ground planes and small circuit patterns close by will not get the same deposit thickness. This was brought out in a black pad study by HADCO if I am not mistaken. By the way is the 4552 committee doing the study on coupons or on unbalanced circuit design as above? Since Peter was observing a problem after 1st pass I felt this is possible as thermal cycling will accelerate oxide production and poor solderability. Anil -----Original Message----- From: Gerard O'Brien [mailto:[log in to unmask]] Sent: Wednesday, November 03, 2004 6:53 PM To: TechNet E-Mail Forum; [log in to unmask] Subject: RE: [TN] Poor ENIG Solderability I must disagree must vehemently, the 4552 committee has tested and continues to test after 38 months of real time storage a 1 micro-inch deposit which continues to solder excellently. Attempting to specify a thickness exceeding a self limiting process will only result in the supplier leaving the boards in the bath longer which has been shown to be more detrimental than advantageous. If you are truly getting an ENIG deposit with wild variations in pad deposit thickness adjacent to one another then CHANGE YOUR SUPPLIER! Gerard O'Brien Photocircuits Corporation Co-chairman 4-14 plating committee. -----Original Message----- From: Anil [mailto:[log in to unmask]] Sent: Tuesday, November 02, 2004 11:46 PM To: [log in to unmask] Subject: Re: [TN] Poor ENIG Solderability Peter ENIG gold thickness is non uniform. Pads with lower gold thickness may exist next to pads with adequate thickness. These low gold pads will bring up nickel oxide in the first pass and be unsolderable in the second. It may be safer to specify more than 0.1 micron gold on the PCBs to get rid of problem the IPC workgroup advises higher. Anil Kher micro interconnexion pvt. ltd D3-12A, Corlim Industrial Estate Corlim, Ilhas , Goa , India 403110 tel: 91-832-2284209/337. fax 2284209/2285271 e mail: [log in to unmask] Leaders in Gold plated PCBs - selective/cob -----Original Message----- From: Peter Barton [mailto:[log in to unmask]] Sent: Monday, November 01, 2004 9:24 PM Subject: Poor ENIG Solderability We have been experiencing poor solderability on ENIG finished PCB's on a sporadic basis for some time now but have never been able to pinpoint the cause. This problem only ever manifests itself at the second side reflow, where solder wetting to pads is very poor, or even non-existent. The problem has occurred on a few different part numbers. Brief details of our process are as follows: Print paste, place and reflow side 1, followed by batch water washing (including D.I. rinse but no saponifier)and dry. Print paste, place and reflow side 2, washing as per side 1. There is plenty of solder paste present on the pads before placement and reflow. Where wetting to the pad is poor the solder has wetted the component lead. The solder paste is a water washable type, within it's expiry date etc. As it is fairly active I expect to have sufficient activity to overcome any minor impediment to soldering. The time before paste printing and reflow has been varied, as has the time between washing the first side and processing the second side. Additionally I have experimented to see if our misprint washing could influence solderability but none of these factors seems to have any significant effect. I have had the water input to the wash process analysed and there is no evidence of any contaminants that may cause PCB surface contamination. In addition PCB's from the same wash batch can vary in solderability. I have had SEM/EDX analysis done on affected samples to determine if the Gold finish may be porous thus allowing the underlying Nickel to oxidise but the lab reports nothing unusual. Analysis has been done at low eV as well as the standard rate for this test. Additionally they report that Phosphorus distribution within the Nickel is not unduly high, or concentrated in any particular areas. One finding at SEM/EDX was the identification of high levels of Carbon and Oxygen - presumably this is an indication of organic contamination? I have researched other possible causes of this problem and understand that it is possible that partially cured solder resist may outgass during the first side reflow, thus rendering the metallised surfaces on the second side difficult to solder. FTIR analysis is being done to try to determine the compounds involved but the lab is new to electronics assembly analysis (as am I) and I do not have many samples for them. I do not have the luxury of sacrificial samples now and still do not have and real insight into my problem. In addition (of course) anything that exhibits this problem is a production board. Can anyone recommend what further tests can be done without having to destroy the assembly. Also are there any other suggestions as to possible causes of this phenomenon? We are based in the UK so any labs that may wish to respond please do so offline. Thanks in advance for any pointers, ----------------------------------------------------------------------- Peter Barton Senior Process Eng ACW Technology Ltd Dinas Isaf West Tonypandy Mid Glamorgan. CF40 1XX Wales Tel: 01443 425200 Fax: 023 8048 4882 International Tel : +44 1443 425200 International Fax : +44 23 8048 4882 Website/URL: www.acw.co.uk --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 -----------------------------------------------------