James & other LFers,
The black pad phenomenon has been much discussed here over the years, so
there is lots of information in the list archives. It refers to the
appearance of the pad after a solder joint has failed, rather than before it
is made. I cannot comment on a pad which is black before soldering.
Best regards,
Roger Bilham
Falcon Metals UK
020 8249 7828
07941 122446
----- Original Message -----
From: "Aston, James" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, January 16, 2006 6:45 AM
Subject: Re: [LF] Gold thickness on BGA ???
Roger, LFers
Could you expand on the 'Black Pad' phenomena you mentioned please?
We've recently noticed a batch of boards which appear to have small
sections of the pads that are discoloured black and would like to know
how detrimental this is, and if there is any risk that the area will
degrade. Note: The black area will not 'tin', but the remaining soldered
joint has wetted to the rest of the pad without any problems.
Thanks
James Aston
Manufacturing Engineer
Engine Control Systems
York Road
Hall Green
Birmingham
B28 8LN
( 44 (0)121 627 6600
( 44 (0) 7868 660495
: [log in to unmask]
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Kane, Joseph E (US
SSA)
Sent: 13 January 2006 15:20
To: [log in to unmask]
Subject: Re: [LF] Gold thickness on BGA ???
Don't know about BGA's, but the gold thickness on component leads
can exceed 100 microinches, or about 2.5 microns. We've done a lot
of measuring, and thickness is typically more than 1 micron.
Much less should be equally effective; does anyone know why component
suppliers use any more than the minimum necessary? Something to do with
the process?
As for bulk solder, I've seen data suggesting a limit of 3% Au to
prevent
embrittlement. Are you suggesting 0.3% for BGA's because of some kind
of stratification?
Joe Kane
BAE Systems
Johnson City, NY
-----Original Message-----
From: Roger Bilham [mailto:[log in to unmask]]
Sent: Friday, January 13, 2006 3:46 AM
To: [log in to unmask]
Subject: Re: [LF] Gold thickness on BGA ???
Ken and LFers,
The gold thickness on components is normally much thicker than on PCB
pads.
From the nosing around that I have done, the thickness reported for
components is between 0.3 and 1 micron and this is deposited by
electroplating. In contrast, the thickness on PCB pads is between 0.05
and
0.25 micron. This is depositied by immersion plating, which
automatically
limits its thickness.
If you calculate the amount of gold in the resulting joint, I would
regard
anything over about 0.3pct Au as risky from a throretical standpoint and
liable to give brittle joints. This is quite apart from the black pad
phenomenon, of course.
Does anyone have practical data to offer?
Regards,
Roger Bilham
Falcon Metals UK
020 8249 7828
07941 122446
----- Original Message -----
From: "Kanaiyalal Patel" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, January 12, 2006 10:28 PM
Subject: [LF] Gold thickness on BGA ???
> Component platting Expert,
> My supplier is saying that they have used Ni/Au (electrolytic
process,
so no P) as the surface plating on the BGAs. The thickness parameters
are 5
um (minimum) Nickel plating + 0.5 um (minimum) soft gold plating.
>
> I think the gold is thicker than what I have seen on PCB which is
normally between 0.0762 - 0.2032 micron (3-8 micro inches). Is this
normal
or do you see any problem with platting thickness as I am seeing crack
along
the component interface?
>
> Re,
> Ken Patel
>
>
>
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