The assumption is always that the bow and/or twist is gradual and more or less consistent over the length or width of the PWB. I think that this allows for sudden steps or non-flat areas over short distances as long as the overall tolerance of .75% is compliant. I feel that the requirement should be measured per sq in. based on the bow or twist total divided by the distance. I usually specify it as .008/ in x in not to exceed .0075 x the length and width. I know that this is NOT how the IPC spec reads, but I feel that is how it should be specified and inspected. Large FPGA type devices can't stand large deviations over short distances.
Is this fallow IPC TM 2.4.22 revision C?
How to measure the bow and twist if the PCB has components already?
Sir what is the acceptance criteria of bow and twist plz tell me with calcuation and formula
0.75 % for smd 1.5 % max for trough hole
The assumption is always that the bow and/or twist is gradual and more or less consistent over the length or width of the PWB. I think that this allows for sudden steps or non-flat areas over short distances as long as the overall tolerance of .75% is compliant. I feel that the requirement should be measured per sq in. based on the bow or twist total divided by the distance. I usually specify it as .008/ in x in not to exceed .0075 x the length and width. I know that this is NOT how the IPC spec reads, but I feel that is how it should be specified and inspected. Large FPGA type devices can't stand large deviations over short distances.
what happen when you have both, twist and bow?
+Daniel CP better reject your board then....