cross section and check your intermetallic thickness.  thermal shock  
and see if you have delamination - if you lost thermal ground, how  
critical it is for your part?  how much design margin you have (50%  
coverage is working at maximum power of device operation temp +  
maximum  environmental temperature with assembly allowed cooling?  
conduction? = it should simulate at end of the life, that mean, you  
should aging the part prior to thermal shock according  to designed  
user life x safety factor.  for example, design for 5 years with  
safety factor of 2 = 10 years... you need to aging equivalent of 10  
years using accelerated IMC growth... use your process control  
minimum acceptable coverage = if you do not have xray data for large  
lot, estimate based on worst case * 80% less... that would be my best  
guestimate)... my 2 cents.
-  ha, forget to mention, assume your plating house gold thickness is  
no change... if there is large variation, bet off... wetting, reflow,  
IMC growth are not predictable...
               jk
On Aug 7, 2015, at 3:25 PM, Ricardo Moncaglieri wrote:

> Estimated colleagues,
> In some cases component´s thermal planes Au finished which will be
> solded on ENEPIG TMM10 pcb where coplanarity is very critical then
> pretining modify undesirably coplanarity.
> Taking into account this fact, we have reflowed the component (solder
> the earth plane to pcb) without pretining and compare soldering  
> under RX
> to another done with pretining. Have found out no difference between
> both cases (with and without pretining).
> Furthermore will run some tracking tests to verify joint.
>
> My question:
>
> Do you know or have any background experience on soldering Au finished
> thermal planes without pretining?
> In all other cases of Au components terminals finished, we always
> remove Au.
>
> brgds,Ricardo
>
>
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