Rich,
the 218 tape I believe is only operating at low temperature of 120 C..
Normally, the kapton can go very high... (even soldering temperature ...some
of them at least).
jk
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]]On Behalf Of Rich Buccieri
>Sent: Tuesday, July 23, 2002 9:16 AM
>To: [log in to unmask]
>Subject: Re: [TN] Conformal Coating repelled by masking
>
>
>Experienced same problem and found that the Kapton tape adhesive
>in deed was
>repelling the coating - solved problem with 3M 218 masking tape.
>http://products.3m.com/us/electronics_mfg/products/electronics_ehp.
>jhtml?pow
>url=VBZVSB2DTFbe54FL4R3WNKgeGST1T4S9TCgvPNTCW5KRV1gl I'm sure there must
>be others that would perform as well.
>
>Rich Buccieri
>Operations Manager
>Techdyne, Inc - Round Rock, Texas
>Phone: (512) 310-9139
>Fax: (512) 310-9138
>E-mail: [log in to unmask]
>
>
>
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]]On Behalf Of
>[log in to unmask]
>Sent: Tuesday, July 23, 2002 5:43 AM
>To: [log in to unmask]
>Subject: [TN] Conformal Coating repelled by masking
>
>
>Hi, Folks,
>
>I have a theory about one phenomenon out of two that I have just witnessed,
>but seek your sage thoughts on the matter.
>
>Our fabrication shop was spray coating an FR4 / HASL-finished board with
>Humiseal 1B31, which was masked with some very expensive Kapton tape. The
>tape is meant to be a no-static, no-residue type. We noticed that, under
>the UV inspection lamp in the spray booth, the coating appears to recede
>from the edge of the Kapton tape - at least there is a "line" 1 or 2 mm
>wide at the edge of the masking, that indicates (to me) a different
>thickness of coating in that zone compared with the rest of the board. We
>tried over-spraying the affected areas again once the initial coat had set
>a bit, but the line reappeared. It only happens where there is Kapton tape.
>
>At the same time, the coating on the solder side of the board is a nice
>shiny finish, while the component side has quite large areas that have a
>more matte, slightly "rough" appearance. I doubt there is a connection
>between the two phenomena, but you never know.
>
>My theory about coating recession from the tape is that there is a static
>charge on the Kapton tape, in spite of the "no-static" presumption, and
>that the coating particles in the spray are likewise charged from their
>passage through the spray gun. The two like charges are then repelling one
>another. I noticed that neither board nor spray gun are grounded, and think
>that they should be (comments, anyone?).
>
>My secondary theory is that the coating is reacting with the tape adhesive
>at the edge of the tape, creating a line of contamination that the coating
>doesn't stick to properly. Kapton tape is a commonly used masking material,
>though, and I haven't heard of this problem occurring with it before.
>
>I haven't come up with an explanation for the matte areas of coating on the
>component side of the board. The board had just come from the customary
>cleaning and drying that I give all boards just prior to coating.
>
>Can you come up with possible explanations and cures for what is happening
>here?
>
>MTIA
>
>Peter
>
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