Dear Mr. Duncan ,
I think your gold is too think when applied in soldering .
Basically , what Zhangshoukai said is correct , there are some report , such
as Hp , has studied such problem and didn't recommend to use ENIG on BGA
application .
James Wang
Assistant Product Manager
Litton - Kester Solder , Taiwan
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of <Peter George Duncan>
Sent: Thursday, July 12, 2001 8:20 AM
To: [log in to unmask]
Subject: Re: [TN] PCB surface finishes
Hi, Shou Kai,
We had a CPU card designed and made for us in the States, and it carries
BGA's - 256 and 388 pin devices. This board has an ENIG finish to provide
adequate flatness for the BGA's - the finish is 4.5 microinches hard gold
over 150 microinches Nickel on a 12 layer FR4 board - quite a thick Nickel
layer, I think, but that's what the designers specified.
Soldering was a concern to me too, with visions of high melting point
solder with silver content and risks of frying dies trying to achieve a
good soldering temperature. But we tried a eutectic solder paste (63/37)
specially formulated for fibre optics work and it worked very well. Wetting
was good, solder joints were properly formed. Peak soldering temperature
was 218 deg C for about 16 seconds, bringing the centre pins of the BGA's
up to 205 deg C.
If your board is in good condition, you should have no problems.
Pete Duncan
Shoukai Zhang
<skzhang@HUAW To: [log in to unmask]
EI.COM> cc: (bcc: DUNCAN Peter/Asst
Prin Engr/ST Aero/ST Group)
Sent by: Subject: [TN] PCB surface
finishes
TechNet
<[log in to unmask]
ORG>
07/11/01
05:27 PM
Please
respond to
"TechNet
E-Mail
Forum.";
Please
respond to
Shoukai Zhang
Dear TechNetters:
As we know that the preferred metal surface finishes are HASL, EN/IG
(Electroless Nickel and Immersion Gold, and OSP etc.
It's reported that EN/IG(also called immersion gold) suface may lead
unreliable solder joint for BGA component, and suggest do not use
immersion gold for designs that have BGAs.
Please give your advices.
Thanks with best regards,
Zhangshoukai, PE, Huawei Technologies.
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