I have been given the priveledge of revising our procedure to comply with J-STD
033. I have come across a couple of problems and hope you can help. First
problem is moisture barrier bag is supposed to have a water vapor transmission
rate of  .002 g/100in sq. But the materials I have found (3M 3300, SCC
DRI-Shield 2000 ) list wvtr of .02g/ 100in sq. and claim to meet the
requirements, is there a typo in the standard?
Next is section 6.3.2.2. To determine how much dessicant to put in a dry pack
bag you must know how much water vapor a unit of dessicant will absorb at 10%
humidity but doesn't tell you how to determine this. Also the formula given, if
you assume that the dessicant will absorb 2.85g of waetr vapor at 10% and that
the WVTR is really .02g/ 100 in sq would require 8 units in a 10"X16" bag,
pretty much the standard size that our IC's come in. Doesn't leave a lot of room
for parts. Our suppliers are only including 1 unit when they package. So are my
suppliers not doing it right or is my math wrong? Thank you in advance.

Charles Caswell
Process Lead, PCB
Frontier Electronics Systems
Stillwater OK.

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