The dull/grainy appearance is normal when soldering gold plated connections.
Questions that come to mind are:  Are you tinning either surface before
soldering?  Is the assembly subjected to temperature extremes?  What is the
Tce differential between the pwb and component body?  Are the components
leaded or leadless?  Is the assembly subjected to vibration or shock while
in the "end-use" application?  Have you microsectioned or otherwise measured
the thickness of the gold on the components & pwb?  All of the above (+
more) are considerations.   In general a gold coating of less than 0.000050
in. is considered insufficient to inhibit corrosion/ oxidation of the plated
surface during long term storage.  Gold thickness of greater than 0.000100
in. is considered excessive and will degrade the mechanical characteristics
of solder connections.  Ideally, for leadless SMT, the plating thickness
would be 0.000075 and you would double tin the surfaces to be soldered.
With a leaded SMT, where the leads provide some compliance to accommodate
Tce differntial and the stress on the connection is thereby reduced, it is
probably OK to tin the leads one time prior to soldering. The goal of course
is to keep the Au content of the connection below 3% and avoid the dreaded
gold embrittlement syndrome.  Hint: In today's world (thanks to better
process controls and the high cost of gold) not many folks put on more gold
than the minimum required (check the thickness) hence it is probable that
the components only need to be tinned once.  The words presently in Rev. B
of ANSI/J-STD-001 (Para. 5.4.1) state: "Gold shall be removed from at least
95% of the surface to be soldered of throughhole components with 2.5
micro-meters or more of gold plating and from 95% of all surface mount
surfaces to be soldered regardless of gold plating thickness.  A double
tinning process or dynamic solder wave may be used for gold removal.  These
requirements may be eliminated if there is objective evidence that there are
no gold related solder embrittlement problems associated with the soldering
process being used.  The objective evidence must be documented and available
for review."   If you meet the abvoe criteria then just change your
inspection criteria to eliminate "bright & shiny" and concentrate on good
wetting and correct quantity.   Hope this helps.  Jim Moffitt/EMPF


At 01:57 PM 9/30/96 PST, you wrote:
>          Does anyone have experience soldering gold-plated SMT components to 
>          gold-plated PCB's using a eutectic (Sn63/Pb37) solder? The solder 
>          joints exhibit a dull, grainy appearance. Although I know that
longer 
>          liquidus dwell times and a maximum reflow temperature of 220 C are 
>          typically recommended when soldering to gold,  will other solder 
>          alloys perform better (i.e,, Indium alloys)?
>          
>          Thanks in advance,
>          
>          Greg Kilinski
>          Acuson Corp. 
>          [log in to unmask]
>
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