Others have responded that the cost of immersion silver is usually much
less than ENIG.
But what you need to consider also is whether to use the nickel with
flash gold, standard electroless nickel/immersion gold (ENIG), or
immersion silver.
When soldering to the immersion silver finish the silver will be
absorbed into the solder and the solder joint will be formed on copper.
With the flash gold over nickel or the ENIG plating the gold will be
absorbed into the solder and you will form a solder joint to the nickel.
Either of the flash gold over nickel or ENIG requires plating of nickel,
and as such the process is susceptible to nickel skips, which you have
already experienced. Not much fun.
The solder joints formed on copper will be stronger than those formed on
nickel because of nickel's much slower rate of dissolution into the
solder joint. Because of the slower dissolution rate, the assembly
requires more heat, and for a longer time, especially under the BGAs.
BGAs do an excellent job of insulating the solder spheres.
If you have BGAs or chip scale components, you will be much better off
with immersion silver finish on the PWB. If you have high impedance/high
frequency circuitry you will also be much better off with immersion
silver.
Buy a sample of boards and qualify the assembly with the different
plating no matter which one you choose.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Sumxplore
Sent: Friday, January 13, 2006 11:55 PM
To: [log in to unmask]
Subject: Re: [TN] enig bad board
Looks like this is the beginning of my nightmare with more to come after
reading those valuable feedback by technetters.
No,I haven't try immersion silver but certainly I will explore it.Anyone
can let me what is the cost differences between Immersion silver and
ENIG?
Thank you.
----- Original Message -----
From: "Lee Parker" <[log in to unmask]>
To: "'TechNet E-Mail Forum'" <[log in to unmask]>; "'sumxp'"
<[log in to unmask]>
Sent: Saturday, January 14, 2006 1:34 AM
Subject: RE: [TN] enig bad board
> Sumxp
>
> It is likely the thickness of the gold is inadequate and the
> underlying nickel has oxidized. I would measure the gold thickness
> (XRF) and compare it to the minimum specified. The silver color after
> erasing is most likely the nickel that is under the gold and with the
oxides removed.
>
> There are many other alternatives these days to ENIG such as immersion
> silver. Have you evaluated into any of these?
>
> Best regards
>
> Lee
>
> J. L. Parker Ph.D.
> JLP Consultants LLC
> (804) 779 3389
>
>
> Best regards
>
> Lee
>
> J. L. Parker Ph.D.
> JLP Consultants LLC
> (804) 779 3389
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of sumxp
> Sent: Friday, January 13, 2006 10:48 AM
> To: [log in to unmask]
> Subject: [TN] enig bad board
>
> Hi,
>
> We noticed few ENIG bga pads black in color instead of gold.It turn
> silver when use eraser to remove away the black color pad.What is the
> defect mode?
> Any reliability issue?Is it advisable to continue using these pcbs?
>
> Thanks......
>
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