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August 2012

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From:
"Whittaker, Dewey (EHCOE)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Whittaker, Dewey (EHCOE)
Date:
Wed, 15 Aug 2012 16:35:09 +0000
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Kevin,

Bob and Joyce made good points. Here is my ranking:

ˇ         Bare copper with a TBD nano-technology OSP

ˇ         ENEPIG

ˇ         HAL with a TBD alloy (snick, etc.)

ˇ         ENIGš

ˇ         IAg

ˇ         OSP



Note 1 - If you have a sufficient volume of business or very close relationships that you feel you are getting their full attention and they have a good history of process control, then this is a good selection.



Dewey





-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Wednesday, August 15, 2012 9:09 AM
To: [log in to unmask]
Subject: Re: [TN] PCB finish: ENIG vs. hard gold



Kevin,



 Add to that the monitoring of the ENIG. If the process is not controlled

you could end up with black pad or other soldering problems.



Bob K.



-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Glidden, Kevin

Sent: Wednesday, August 15, 2012 12:01 PM

To: [log in to unmask]

Subject: Re: [TN] PCB finish: ENIG vs. hard gold



Thank you, everyone, for your responses.  To summarize (and ensure my

understanding is correct):



"Hard Gold" is essentially electroplated gold that is co-deposited with

other alloying metals (nickel and/or cobalt) to make it "hard".  This

plating is primarily used for gold-finger edge card contacts, and not

soldering.    Many responses indicated that due to the alloying metals,

these surfaces are not at all solderable.



The distinction is that "soft gold" or "gold flash" [which may be  what the

PCB supplier actually meant to say] that is also electroplated can typically

be soldered to, but has some key disadvantages to ENIG, such as:



- the ENIG immersion gold process is self limiting and as such results in a

uniform plating thickness, whereas the electroplated gold final thickness is

dependent on many factors such as plating chemistry cleanliness, geometry,

current density, processing time, etc, etc.  The concern is that too much

gold can cause gold embrittlement of the solder joints (weak solder joints)

as the gold itself "dissolves" into the solder joint mass during the

soldering process.    The max thickness recommended is 4 to 8 microinches

(vs typical 3-5 microinches for ENIG), which requires strict process

control.



- the ENIG process results in better uniformity, whereas the electroplated

gold has a higher porosity, which in turn can result (particularly at

thinner deposit thickness) with less protection for solderability, reduces

shelf life, etc.



- the ENIG process results in higher purity gold, as it is chemically

induced.  The electroplated gold typically has a lower purity as other

conductive metals can co-plate in solution.



- the ENIG immersion gold process results in gold plating over the pad edges

as well as the lands, whereas the elctroplated covers only the lands and

would leave bare copper on the pad edges.



Based on these points and the responses, it seems ENIG is the better and

safest choice.





From: Glidden, Kevin

Sent: Tuesday, August 14, 2012 12:12 PM

To: [log in to unmask]

Subject: PCB finish: ENIG vs. hard gold



Hi everyone,



We have a PCB supplier who is offering "Hard Gold" as an alternate to ENIG

finish, due to PCB size and processing capabilities.  The application is

Class 3 (mil/aero).  The circuit is thin FR4 and subject to SMT reflow w/

Sn63Pb37 (non RoHS) solder alloy, and moderate flexing in end application.



Can anyone offer info on the differences between the two finishes, and/or

their suitability?  Is there an IPC spec (or specs) that outline "hard

gold"?



Thanks,



Kevin Glidden





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