In order to burn away PCB surface material several things must be present:
A moist environment for several min at a time.
Repeated moist environment episodes in the presence of voltage and current.
An external supply of energy for a 1.574 mm thick FR4 laminate in the neighborhood of 39 J for 9 s to ignite and 47 J to sustain a flame for 11 s that is capable of carbonizing the material. For a 1.574 mm thick CEM-1 laminate this can occur with 27 J for 6 s to ignite and 157 J to sustain a flame for 35 s that is capable of carbonizing the material. See experiments #5, #9a and #9b of Chap. 14 for comparative details.
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