|Ask the Experts|
February 23, 2011
J Lead Overhang Specification
|Expert Panel Responses|
Per IPC-A-610 Rev E, page 10-44, " Although not rated for dielectric strength, and therefore not satisfying the definition of an "insulator or insulating material," some solder mask formulations provide limited insulation and are commonly used as surface insulation where high voltages are not a consideration." Hence, solder should not be used as an insulator. If the lead extends over the conductor as shown in the picture, one has to define the minimum electrical spacing and this spacing will apply to the distance between the pin and the conductor trace beneath the solder mask. If the solder mask is to be used as an insulator then the electrical and dielectric parameters have to be specified on the master drawing.
Vice President, Technical Director
This user needs to refer to IPC-2221 section 6.3 "electrical clearance".
Regional Sales Manager
OK International Inc.
According to J-STD-001D Table 7.7. the toe overhang must not violate minimum electrical clearance. In this case I would estimate the designed clearance has been reduced and this would thereforebe unacceptable. Also, solder resist can not be relied on to provide electrical insulation since it tends to be thinner along track edges etc and breakdown can therefore occur.
Principal Engineer - CMA Lab
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