Dear Collegues,

The gold content in tin-rich solders should be restricted till 3 w/w%
with penalty of increased chance of brittle solder joints. Over 5 w/w%
of Au, the chance of knocked off components, as Sani described, after
1 week in stock is more than 25% (personal experience). So you have to
calculate how much solder paste you need on your NiAu metallisations.

Soft Soldering Processes
Peer Langeveld, Consultant



2007/3/26, Paymon Sani <[log in to unmask]>:
> 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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