Entek Plus data spec from Enthone specified a coating
thickness of 0.35um (min 0.2um to 0.5um max).  My pcb vendor
follows this thickness req. and performs a UV
spectrophotometer test as per a batch cycle to measure the
coating thickness.  (By the way the vendor uses dip-tank process
for coating Entek-Plus)  I am seeing brown residues on TH
solder joints (not on smt solder joints after reflow) after
wavesoldering.

I am drawing a conclusion that the cause of brown residue is as
the result of much thicker coating in plated TH holes.  I believe
heat and flux (2% no clean flux) do not have a time to dissolve
and evaporate the coating in plated TH holes.  Semi-dissolved
coating in TH holes gets pushed up toward the component side
by molten solder.  Thus causing spotty brown  residue on TH
solder joints on the component side of boards.

The reduction of belt speed (3.5ft/min) and some heat increase
do not reduce this residue.  Hand-soldering of TH holes were
performed with the same result as per previous e-mail
message.

I wish I had a damn micrometer to measure that coating
thickness, or Is there more stuff???

regards
Matthew Park
NII Norsat International Inc.

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