Ben,
Here is the message that you sent to me. I would have responded sooner,
but the network was down Friday and my e-mail as well. I usually get a
message stating that my message was distributed to 500 some odd members,
but I do not receive it myself. We are investigating the immersion gold
option. My reservation in that option is the gold plating thickness and
the possibility of hardware scoring the gold away and exposing the
copper beneath. I understand that nickel shall be between the copper and
the gold and this may be sufficient. I'll keep you posted, Ben. Thanks
for the references. How may I obtain them? You know that I like to
collect that sort of thing...
Chris Taylor
LXE, Inc.
125 Technology Parkway
Norcross, GA 30092
(770) 447-4224 X3242 v
(770) 447-6928 f
[log in to unmask]
>----------
>From: Davis Ben[SMTP:[log in to unmask]]
>Sent: Thursday, May 14, 1998 7:08 AM
>To: [log in to unmask]
>Subject: Re: [DC] OSP Over Hardware Ground Lands
>
>PLEASE forgive me if this is posted twice. I got "undeliverable
>message" the first time around...
>
>Taylor, Chris H. wrote:
>>
>> With the use of OSP becoming more commonplace, a concern has been raised
>> as to how chassis ground lands surrounding hardware mounting holes are
>> protected from corrosion in a high reliability commercial assembly. Is
>> OSP adequate for long term corrosion protection for a ground land? Per
>> my understanding, OSP is used to provide short term protection to SMT
>> lands, has a shelf life and is not intended to be left on the PCB
>> assembly after SMT reflow.
>>
>> In the past, HASL (hot air solder leveled) was adequate in providing the
>> necessary corrosion protected metallic contact for hardware conducted
>> chassis ground. If a PCB is produced with OSP instead of HASL, then
>> there is no provision for the ground lands to be solder coated. One idea
>> that comes to mind is to include the lands in the solder paste artwork.
>> Is this practical? I realize that the PTH (plated thru hole) will still
>> lack solder coating, but a circular relief can be provided within the
>> land and around the hole to allow it to be an NPTH (non plated thru
>> hole).
>>
>> How are my colleagues addressing this issue?
>> Chris Taylor
>> LXE, Inc.
>> 125 Technology Parkway
>> Norcross, GA 30092
>> (770) 447-4224 X3242 v
>> (770) 447-6928 f
>> [log in to unmask]
>>
>
>Chris...
>
>We have not used OSP on our boards, but our assembler has asked us to
>use immersion gold (2 - 7 microinches over nickel). I just received
>some info on the process (from Tyco in Utah) and supposedly the cost the
>same (from this board mfg) for HASL, immersion Au or OSP. A couple of
>the advantages are no special handling, no shelf life control and added
>strength in PTH barrels from the nickel. The only drawback I can see is
>possible solder bath contamination.
>
>A couple of technical papers were mentioned:
>1. "An Investigation into the Characteristics of Solderable Coatings
>for Printed Circuit Boards", K.J. Whitlaw'
>2. "Effect of Au on the Reliability of Fine Pitch Surface Mount
>Joints", J. Glazer, P.A. Kramer and J.W. Morris Jr.
>
>I'm sorry this doesn't address your question directly, but I think it
>provides an option that might help with the problem. You might want to
>check with your vendors to see if they have immersion gold capability
>and if it is a cost adder.
>
>
>Ben Davis
>Systems & Electronics, Inc.
>[log in to unmask]
>
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