Solderability Failure at heel area

I am a plating engineer currently I encountered solderability failure in the heel area in our production line. No marked of over pressing is seen the heel area but the failure is all in the heel side. Why always in the heel encountered de-wetting?

Ella,

Said portion of leads come into contact with the form punch and the anvil of TnF process. Based from an MPCpS study that we have completed, this step contributes to thinning of Sn layer thickness. If you will cross section the formed leads you may find that the thickness in this area will be thinner compared to other parts. This will become worse if the plated parts that you mentioned pass through post plate bake process prior to TnF. To solve this we have optimized (MPCpS) the TnF - improved the form punch and anvil design and mechanism. Temporarily though you can increase a bit the thickness of plating.