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OSP (Organic Solderability Protectant)
coating is increasingly being used due
to the advantages they offer the PCB manufacturing
process. By preventing oxidation of bare
copper pads, OSP offers the elimination
of the bare board solder-coating process
(HASL -Hot Air Solder Leveling), and allows
multiple passes through reflow ovens without
degradation of solderability.
The OSP coating is dissolved by the flux
when solder paste is applied to the pads
and should not create an insulating barrier
to the test probes. However, in cases
where a PCB has components on only one
side and test points on the other, bare
copper pads coated with OSP remain as
test points. Reliable penetration of this
coating by the test probe is required
to test the PCB, which should not be a
problem if thickness and temperature is
controlled in the OSP coating process.
The coating thickness recommended by OSP
manufacturers is between 0.25 and 0.35
microns. Higher contact pressure such
as 6 to 10 ounces consistently provides
a more reliable contact when the thickness
of the OSP is greater than the specified
0.35 microns. Therefore the use of higher
spring forces may be the best testing
option.
Generally, the same tips used on no-clean
flux processes are recommended such as
the 51, 53, 61, 63 and 91. QA typically
recommends using these tip styles in our
steel option. |
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