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March 2007

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Subject:
From:
Paymon Sani <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Paymon Sani <[log in to unmask]>
Date:
Mon, 26 Mar 2007 12:29:16 -0400
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text/plain (193 lines)
Hello Christopher,

IPC-4552, Specification for ENIG process does not specify a value for
your question below. IPC suggests a minimum of 2 uin at four sigma below
the mean; the typical value is 3 to 5 uin to provide good solderability
to the Nickel layer within 1 year after the PCB fabrication.

In the past, we experienced brittle solder joints with gold that was 12
uin thick. The parts fell off the assembly when it was knocked against a
rigid surface such as the top surface of a table.

If you can not find a good answer to your question then you may decide
to create a DOE to model the relationship between the gold thickness and
the hardness of the solderjoint. This would be a good project for an
undergraduate engineering student!

Hope this helps,
Paymon Sani



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Christopher Nash
Sent: March 26, 2007 11:42 AM
To: [log in to unmask]
Subject: [TN] Gold %

Hello all, what is the IPC standard for the acceptable level/percentage
of
gold that can be consumed into a solder joint before gold embrittlement
becomes an issue?  

Christopher J. Nash 
Mid-West Technical Support Engineer
Indium Corporation of America 
Phone #: (315) 853-4900 x7521
Fax #: (315) 853-1000
www.indium.com

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Monday, March 26, 2007 11:33 AM
To: [log in to unmask]
Subject: Re: [TN] Press-fit Soldering

Jumper mods can be made to standard compliant press-fit pins. However,
unlike conventional pin-through connectors, you may not be able to
rework (to remove) the connector should you ever need to. This is
because standard solder removal methods such as wicking or solder
suckers will not be able to remove every bit of solder where the
compliant pin makes contact with the hole wall.
Do not think that if you apply solder sparingly, you will not fill the
hole and thus will not solder the compliant pin to the hole wall. If
either the connector pin or the hole has any tin or tin/lead finish,
simply touching a solder iron to the pin will be enough to solder the
pin to the hole wall by reflowing the plating finish.
But if you have to add the jumper, make sure the assembly has passed all
electrical testing first. I am assuming you wish to put the jumpers on
the solder side of the assembly.
If, however, you wish to solder to the top side, then wrap and solder
around the pin up away from the pad (if possible), and perform soldering
only to meet the wrap-and-solder criteria, where the wrap must be a
minimum of 3/4ths of the way around the pin, the soldering must be such
that the lead contour is visible, and the insulation of the jumper
begins a maximum of one wire diameter from the solder joint. A heatsink
clip should be positioned where the pin enters the pwb to prevent the
plating from getting hot enough to reflow, if needed.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Barr
Sent: Monday, March 26, 2007 11:07 AM
To: [log in to unmask]
Subject: [TN] Press-fit Soldering

Hi All,

Engineering wants to solder a few jumper wires to press-fit pins on
production boards. I am not completely comfortable soldering to
press-fit pins and want to get input from others because there appears
to be conflicting information between previous posts on this subject and
IPC-610.

I have read concern that the heat from soldering (hand soldering in this
case) may compromise the press-fit connection - the theory being that
the hole is already physically deformed and under some degree of stress
by design of the press-fit pin and that heat may produce additional
unintended stress. Since we are soldering a jumper wire the entire hole
will not be filled and there will be a limited amount of heat
introduced. Having never seen rework wires soldered to press-fit pins on
production boards, I don't know if this is really a risk. Has anybody
done this? The connector vendor is not willing to comment because they
don't have information about this, so that adds to the unknown.

The second issue I have read about is that the design of the press-fit
connection prohibits the formation of a properly wetted solder interface
between the pin and plated through hole. Since we are talking about a
solder connection to connect a jumper wire to end of the pin and not for
an electrical connection of the pin to the board I don't think this
applies to our case.

On the other hand, IPC-610 does have a section (4.3.2.1) that gives
criteria for soldering press-fit pins so they must think it is OK. It
states that press-fit pins are not intended to be soldered, but if
soldering is required it gives criteria.

So, my quandry is...is soldering jumper wires to press-fit pins a risk
or not?

Thanks in advance for any and all help.

Bob

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