We are using 170 deg C IPC 4101/24  material for making hi reliability PCBs. The PCB coupons are subjected to 
6X Solder Dip to access PTH integrity & laminate integrity. 5X R/W also carried out. 

to achieve this initial laminates(cores) are baked at 140 deg C for 4 hours. 
after blak OXIDE  baked at 140 deg C for 4 hours
after MLB pressing baked at 140 deg C for 4 hours
after electroless copper plating baked at 140 deg C for 4 hours
prior to HASL baked at 140 deg C for 4 hours
a total of 20 hours at 140 deg C baked during fabrication.


after PCB fabrication. the coupon is separated from PCB and the coupon is baked for 12 hours at 120 deg C. 

The coupon is subjected to 6X solder dip & 5x R/W simulation. 

My doubts are 

Q1. These extra long hours of baking will deteriorate the chemical & mechanical properties of the laminates ? 
      if so , what are the properties are getting affected. The material dicy cured FR4. 

Q2. Whether Test coupon results will reflect the quality of PCBs ?.


R.Saravanan