The situation I have here is that a customer of mine has rejected a lot of our 
PCB's at incoming inspection for SMT pads that did not all wet during their 
solderability test. They are thus, not accepting the product. They sent samples 
back to me for analysis; the samples did indeed show random non-wetted pads 
after their test. The board is a double sided with SMT pads on the top side, 
.130" overall thickness, solder mask used is Probimer 52 from Ciba Geigy.
 
I took one of the pcb returned that had not been tested for solderability and 
measured random smt pads for solder thickness, the results were an average of 
142f", this indicated to me that there was plenty of solder and the possibility 
of intermetallic growth a non issue. I then took the pcb's that the customer 
had done the solderability test on and measured the smt pads that appeared not 
to wet, the results were an average 337f". 

I then took one of the raw pcb's to have our lab do the solderability test the 
specification is as followed: solder pot temp: 474 +/- 8 degree F, Flux 
mixture:650 ml flux (type R rosin), 433 ml isopropyl alcohol (99%), Once per 
week, the older solder is bailed out and a minimum of the pot volume is filled 
with new solder. The test is as followed:1.) Immerse the sample for 10 seconds 
in the flux mixture. 2.) Skim the dross off the top of the solder within 10 sec 
of running the test. 3.) Slide the sample onto the surface of the solder using 
tongs. Allow it to remain on the surface for 10 sec. 4.) Slide the sample off 
the surface of the solder. Place it on the workstation to cool. Immerse the 
sample in isopropyl alcohol. Following this procedure on the raw pcb resulted 
in all smt pads wetting.

The lab tech then took another raw pcb and folloed the same steps as above, but 
this time used R-Rosin flux non-activated. The results: We were able to 
duplicate the same results as our customer samples. Our customer used a non-
activated flux, Rosin flux 25%, 75% isopropyl Alcohol. 

My question is: Would this lack of wetting on random pads actually cause an 
assy issue on the line with regards to solderability of components? Please let 
me know what your opinion is on this.

Thanks,
Dale