Are we sure it is by volume, or is it by weight? I've used the 2%, 3%, or 4% rule by weight. (Threshold depends on application and use environment.) Glenn -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Ryan Grant Sent: Friday, August 19, 2005 10:25 AM To: [log in to unmask] Subject: Re: [TN] max thickness electroplated gold Hi Guy, Its not a rule of thumb, its science... Gold embrittlement happens at 4% gold per volume of tin for eutectic Tin/Lead solder. Clearly this rule isn't a sharp "edge" so I'd recommend a safety margin. Now lets do the math... Assume the component pad size is a 1:1 ratio to printed pad size. Volume of the gold (V_g) = l*w*h_g (length times width times gold thickness) Volume of the solder (V_s) = l*w*h_s*.5*t_r where .5=close approximation of solder powder volume to printed paste volume and where t_r= tin ratio of the alloy. Since we are looking for the ratio where V_g/V_s = 4% as the drop dead ratio, and Since we assume component pad size is 1:1 to printed pad size, l*w cancels out. We now have h_g/(h_s*.5*t_r) = 4% Solve for h_g = .04*h_s*.5*t_r If we assume a 5 mil stencil h_g = t_r*.0001 Assuming Tin/Lead solder at 63/37 h_g = 0.000063 = 63uin That 63uin includes both component and PCB pad gold thickness. That said, your 50 to 100 micro inches is bad news... By the way, if the component is BGA, it comes loaded with a lot more solder, thus the calculation will need to include the volume of the BGA ball. If you are using Lead-Free solder, this rule doesn't apply and transferring principles becomes complicated. The 4% rule is known to apply to silver as well, but you will notice Lead-free alloys are already at a 4% ratio of silver to tin but do not exhibit the same embrittlement failure implied with Tin/Lead embrittlement. The specific point that gold, or silver, embrittles a Lead-Free solder joint has not been studied and published, as far as I know. (If anyone knows otherwise, please let me know the reference). Good luck, Ryan Grant -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey Sent: Thursday, August 18, 2005 2:38 PM To: [log in to unmask] Subject: [TN] max thickness electroplated gold Many of our customers are using the old MIL-STD-275 to specify gold thickness for Hard Gold. They are ordering this because they are doing both wafer and package testing at the die and device level. So, we are seeing 50 to 100 uin of gold over nickel. It hasn't been much of an issue because we build most of the boards by hand soldering methods. We are starting to see components in the parts list for these assemblies that cannot be installed with hand soldering methods. When we solder with printed paste and reflow methods we see dull, grainy joint that are clearly contaminated with gold. When we hand solder this condition is not evident. (I believe the condition may actually be worse because the dissolved gold is more concentrated near the bottom of the fillet. But, that is another discussion). Does any one have a rule of thumb for the maximum thickness of electroplated gold on land patterns intended to receive SMT components . . . say, 0402 passives or MLFs? --------------------------------------------------- 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 -----------------------------------------------------