How can you have large AuSn platelets on the BGA balls? What kinda balls are that? Never seen such.
Anyway, if they exist on the surface, the bulk is probably free from crystals. AuSn platelets on the surface does not have any detrimental effect on the resulting solder joint. Furthermore, IF you see AuSn platelets on the ball surface AFTER soldering, you may still not have a problem, because the volume of interest is the interface between the ball and the board pad. If no platelets exist in that inteface, nema problema. Myself, despite what I say, I wouldn't accept a lot of goldtin crystals on the balls, not for MIL products, because something is anomalous in the process, wouldn't risk anything for products that are made for functioning 20 years.
/Inge
PS. You are the only one I know with golden balls.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: den 16 januari 2008 22:32
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold Intermetallic
So just so I have this straight, if we had, for instance, large AuSn platelets on the surface of a molten BGA ball they should not stop proper connection of molten solder paste to the ball, but if they do not dissolve in the fresh source of gold free solder they could cause problems for the completed solder joint. Is that a fair statement?
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hfjord
Sent: Wednesday, January 16, 2008 4:09 PM
To: [log in to unmask]
Subject: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold Intermetallic
Not really true, the Scottish blood in my veines tells me to be careful with money, the kyrgise blood makes me crush the table, therefore, noone can actually be under it.
I think there are pictures from my large AuSn platelets somewhere on Gregory's wall. If not, I can probably dig them up again from some old report. If such crystals are abundant in a solder joint, the components may just jump off the board when giving a mechanical shock.
/Inge
-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Werner Engelmaier /*
Skickat: den 16 januari 2008 20:30
Till: [log in to unmask]
Ämne: Re: [TN] SV: [TN] Solderability of Tin-Gold Intermetallic
Hi Inge,
As usual people are well advised not to argue with a (this) Swede; 1) he usually knows what he is talking about, and 2) if not, he will drink you under the table.
The IMCs formed by Sn/Pb, and Sn/Ag as well, are platellet-shaped crystals (in cross-section they may look like needles but are always plateletts), and I have seen no evidence that they are solderable. Solderability simply depends on how much Sn, or SnPb, to which you wet, is present. So the amount of these IMCs affect both solderability as well as Au/Ag-embrittlement.
Inge, how is Gerd? I sure have not heard anything about him for some time.
Werner
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