Matthew Park wrote:
>
> 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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> ################################################################Matthew,
Call the company ECI. this company manufactures an instrument that can
help you measure the osp coating thickness.The principle is based on a
sequential electrochemical reduction analysis, or SERA for short.
Good luck.

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