Hi Reuven,
You are correct; the process windows are narrower with LF solders. Good 
LF-solder joints do not show large reliability differences in accelerated testing; 
under some conditions they give somewhat better reliability, in others 
somewhat worse. The complaints relate to the grwater difficulty in achieving good 
quality SJs.
The 50%/75%/100% fill has nothing to do with SJ strength; SJ strength. given 
good wetting   is always more than adequate, with the possible exception of 
unsupported hole SJs. It has much more to do with the reliability if the PTH 
barrel, but for most applications even Class 1 is o.k. The concerns concentrates 
on severe use conditions such as automotive, military, and some industrial 
uses.

Werner



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