Hi Paul, We generally use SiC for grinding unless we have lots of alumina or something super-hard to cope with in which case diamond film can be helpful (although expensive and you need to be really careful with edge of your specimens so as not to catch an edge and wreck the film). From there ever smaller diamond (usually 3micron and 1micron) followed by silica and/or alumina suspension for finishing. Like most, we have a range of different "recipes" to get the job done on a wide range of samples. BR Stewart Stewart McCracken MCS Ltd. Centre House Midlothian Innovation Centre Roslin Midlothian EH25 9RE m. +44(0)7711 541735 t. +44(0)131 440 9090 f. +44(0)131 440 9085 e. [log in to unmask] w. www.themcsgroup.co.uk -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Edwards Sent: 11 June 2010 17:35 To: [log in to unmask] Subject: Re: [TN] Weird formation of voids Just out of curiosity is every one using SiC instead of diamond for cutting and lapping? Paul Paul Edwards Surface Art Engineering -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian Sent: Friday, June 11, 2010 8:52 AM To: [log in to unmask] Subject: Re: [TN] Weird formation of voids Steve, Good observation! This is one of the things that lead my lab manager to determine that the voids were an artifact of preparation and were not caused by the solder paste and/or manufacturing process. The re-polished samples look GREAT. Bev RIM -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory Sent: Friday, June 11, 2010 11:47 AM To: [log in to unmask] Subject: Re: [TN] Weird formation of voids Another thing that's weird, is that you see the intermetallic layer even where the voids are...how does that happen? Steve -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Stewart McCracken Sent: Friday, June 11, 2010 11:36 AM To: [log in to unmask] Subject: Re: [TN] Weird formation of voids Importance: High Hi All, Looks as though sample preparation condition is less than ideal. Sample is a little rounded and it appears that the voids might in fact be embedded debris from the polishing equipment(?) I'm sure Vladimir would agree - get it in the SEM to be sure! Need some better imaging and if possible EDS - these will go a very long way to confirming what's going on. Lumps of silicon carbide can really make a mess of a x-section. If you don't have access to a SEM, you could etch the structure and look for abnormal /unusual structures surrounding these features. Etching would also help to refine the soft edges on a x-section (provide a more natural edge) and let you see if you have shrinkage or gas voids (look at shape) filled with grinding debris. Contaminated mats on a polishing station could explain the pattern of occurrence and the feature. As always though, more info about condition would make diagnosis easier! Kind regards, Stewart Stewart McCracken MCS Ltd. Centre House Midlothian Innovation Centre Roslin Midlothian EH25 9RE m. +44(0)7711 541735 t. +44(0)131 440 9090 f. +44(0)131 440 9085 e. [log in to unmask] w. www.themcsgroup.co.uk -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of stephen gregory Sent: 11 June 2010 16:21 To: [log in to unmask] Subject: Re: [TN] Weird formation of voids Hi Bev! Got your picture today, and have it posted now: http://stevezeva.homestead.com/Bevs_Ball.jpg Almost looks like little pieces of dross. I wonder if something is going on with the solder paste? Or leaded reflow profile with a lead-free BGA? Steve --- On Wed, 6/9/10, Bev Christian <[log in to unmask]> wrote: From: Bev Christian <[log in to unmask]> Subject: [TN] Weird formation of voids To: [log in to unmask] Date: Wednesday, June 9, 2010, 9:51 AM TechNetters, I am sending a picture to Steve to post. I have labs in three locations. One of them has seen weird voids in cross-sections of BGAs while the other two locations have not. For the lab that has seen them, the cross-sections were prepared by different people on different days for different products, using the same equipment. The voids are not in all balls cross-sectioned but may be only in one of two of the balls in a row of multiple solder joints examined. Have you seen anything like this? Do you know the root cause? Vlad, You know what is going on, so please don't respond. 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