Hi Murlidhara, HASL operation itself being very old in the industry, also has its advantages & disadvantages. The spec. for the HASL thickness within a pad & across various other pads varies from customer to customer, depending on their process, application etc., & that is the reason the HASL thickness spec. in general has a wide variation from 50 or 100 micro inches minimum to 1000 or 1500 micro inches maximum, that is the nature of the beast. In general, since the HASL operation is dependent on the pad size - smaller fine pitch devices tend to get thicker solder & as the pad size increases the solder distribution across the pad would tend to get more even & also you would get the thinnest solder deposit at the centre of a large pad. So writing a spec. for HASL has to be very general. Also if one uses vertical HASL compared to horizontal then you would different results. The other thing is where on the pad you measure the thickness - normally the edges, especially the two corners of a pad would tend to be thicker compared to the centre of the pad. The east & west pads of a QFP device would be thicker than the north & south pads depending on the direction of the board through the HASL machine. Hence most of the customers would spec. in such a way that you measure the thickness across various pad sizes starting from a fine pitch device to a large pad on the board & the thickness would have to be measured across the geometric centre of the pad or taking the average of the four corners & centre of the pad. Some of the critical customers would also ask for measuring the highest & lowest point within a pad & the variation should not be greater than 250 micro inches, or a different number depending on the device, application & process used. Hope this helps. Thanks, Krishnan SANMINA-SCI -----Original Message----- From: Murulidhara [mailto:[log in to unmask]] Sent: Saturday, February 05, 2005 4:11 PM To: [log in to unmask] Subject: [TN] Hot air leveing for SMD - specification Dear Technetters, I want to know wheteher there is any specification for hot air leveling operation for PCBs with SMD? What is the level difference allowed from pad to pad and what is the level difference allowed within a pad? Thanks in advance. Regards, Murulidhara.S -- This message has been scanned for viruses and dangerous content by OpenProtect(http://www.openprotect.com), and is believed to be clean. --------------------------------------------------- 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 ----------------------------------------------------- ____________________________________________________________________________ _ Scanned by Sanmina-SCI eShield ____________________________________________________________________________ _ --------------------------------------------------- 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 -----------------------------------------------------