LOL.
I want to make sure nobody takes me too seriously. 
And Ron, I sure did not mean to poke fun at you. My sincere apologies if I came across that way.
I was simply trying to state that BP and BN don't occur as often as they used to; the point is that nickel is not an optimum surface finish for BGA soldering. Other finishes should be evaluated first if the application warrants it. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hfjord
Sent: Tuesday, February 19, 2008 8:43 AM
To: [log in to unmask]
Subject: [TN] SV: [TN] Best surface finish for BGA

The amount of nickel that dissolves from the fork when eating pasta is negligible...correct, no intermeatballic layer will be created.
/Inge

-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Whittaker, Dewey (EHCOE)
Skickat: den 19 februari 2008 15:12
Till: [log in to unmask]
Ämne: Re: [TN] Best surface finish for BGA

Do you know that from pasta experience?
Dewey

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, February 19, 2008 7:02 AM
To: [log in to unmask]
Subject: Re: [TN] Best surface finish for BGA

There is also always a chance of being hit in the head with a meatball launched by illegitimate offspring of R. Crumb.
Even without the black pad or brittle nickel issues, obtaining a good IMF with nickel is more difficult than with copper, especially underneath BGAs.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ron Peeler
Sent: Tuesday, February 19, 2008 7:22 AM
To: [log in to unmask]
Subject: Re: [TN] Best surface finish for BGA

Immersion Silver has worked the best for me.  With Gold there is always of black pads.  I like to best avoid that....

Ronald D. Peeler Jr., B.S. IE
Process Engineer
SWEMCO
Moorestown, NJ 08057
Tel: (856).222.9900 ext. 31
Cel: (484).948.0779
Fax: (856).222.0700
[log in to unmask]



-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Leland Woodall
Sent: Tuesday, February 19, 2008 8:20 AM
To: [log in to unmask]
Subject: Re: [TN] Best surface finish for BGA


We're moving into this technology within the next year or so, and currently use OSP in our lead-free processing.

Are we going to have to change our board finish in order to accommodate BGAs?

Leland Woodall

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, February 19, 2008 7:52 AM
To: [log in to unmask]
Subject: Re: [TN] Best surface finish for BGA

I do not know a lot about the differences between the application of gold flashing over nickel, versus immersion gold over nickel. In either case the soldering is done to the nickel underneath the gold, not to the gold itself which will be absorbed into the solder during reflow. For BGAs, soldering to the nickel requires a much hotter temperature profile due to nickel's slower rate of dissolution into the solder joint.
Apparently your assembly house is discovering this also. 
You have two options. 
One is to suggest to the assembly house that they check their profile with thermocouples placed up through the bottom of the board into the solder ball of one of the BGAs near the center of the assembly. As you can see by Werner Engelmaier's comments on this forum yesterday, the temperature must be close to 255 deg. C if you are using a SAC 305 alloy solder paste and SAC solder ball alloy. Make sure the BGAs are in fact SAC alloy, and not 63/37, if you want a RoHS-compliant product. Mixing SAC alloy and 63/37 balls, or vice versa, will lead to problems with BGAs soldering properly.

The second option is to qualify the product using a different finish. I would recommend trying an immersion silver finish. It usually performs much better, especially when soldering many BGAs with high-density BGA pads. However, only you can tell if this finish is appropriate for your particular product. If it is, you gain the advantage to soldering to the copper underneath that silver finish.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Greaves, Bernie
(IMP)
Sent: Tuesday, February 19, 2008 12:20 AM
To: [log in to unmask]
Subject: [TN] Best surface finish for BGA

The question has been raised here, what is the best gold finish for high
density BGA pads - Immersion gold or gold flashing?   Keep in mind it
needs to be an RoHS process.  Or is there another finish more suitable.
It has come up as a result of our pcb contractor having difficulty with some BGA's taking.
 
Regards,
 
 
Bernie Greaves

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