When exposed metal( contact part of a terminal, solder junction, metal just out of the QFP body, pins in a connector... ) is plated with less than 3% Pb and is mostly Sn, the risk of whiskers is substantial. Increase the percentage of Pb of exposed metal and things change. CC mitigates but not eliminates the problem. Regards, Ramon -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Dale Ritzen Sent: Thursday, May 10, 2007 1:47 PM To: [log in to unmask] Subject: Re: [TN] PCB assembly for medical devices So, the implication is below (2) that the use of a Pb-free tinned part is okay if a tin-lead solder process is used for the junction (with the exception of Pb-free BGA devices) - correct? That is, as far as tin whiskers go... The amount of tin provided by the tinned lead during the soldering process is negligible when using Pb37/Sn63 solder to make the junction. And the amount of Pb in the junction maintains roughly the same amount of tin whisker suppression as we used to enjoy before the Pb-free nonsense began. Correct? Dale Ritzen Quality Manager Austin Manufacturing Services -----Original Message----- From: Louis, Edwin @ CSE [mailto:[log in to unmask]] Sent: Thursday, May 10, 2007 12:06 PM To: [log in to unmask] Subject: Re: [TN] PCB assembly for medical devices If the customer is requiring no pure Tin finishes then you will have to do one of the following operations: (1) buy components with a Tin/Lead finish, (2) Use a Tin/Lead process, (3) replace the Tin or or Lead-free Tin alloy with Tin/Lead by robotic Tin/Lead dipping per the TMTI approved process up to the body or chemically strip the Tin finish and Tin/Lead dip the leads.AVX and Kemet both offer their full line of chip caps and chip resistors in Tin/Lead finish. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of BADRI Sent: Thursday, May 10, 2007 9:01 AM To: [log in to unmask] Subject: [TN] PCB assembly for medical devices Dear All, We have just started assembling some PCBA's to a medical device manufacturer. They hate lead free. The question is as follows: The components are leadfree and the paste used is leaded. Is it ok or do I have to pretin all the components with lead and then process. We have processed couple of boards without pretinning and we have not faced any issue. Will the devise manufacturer accept it. Please advise on the right process. 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