Steve

Ok, let's make a complete list of things to check.

The tape... was it an old roll, or a new roll, do you have lot control on
shop supplies and process materials, could this be from a lot not
recently used???
The operator... was this assembly taped by the usual person... did they
notice anything different, warm boards, wet boards, funny smell???
Raw boards... are they from a new lot date code, or new vendor. Do they
look or feel different?
The conformal coating...  new batch??, old batch, what about the thinner,
same questions, anything else added to the mix than CC and thinner.
Did the spray operator change?? did the operator notice anything
different, did anything happen?? did they spray, strip, clean, bake and
spray again, without retaping to save time???
Spray equipment maintenance... did the equipment get cleaned just before
this happened... what kind of cleaning fluids were used???
Pre-masking cleaning... anything happen here,
is there a Pre-bake before masking, or did somebody skip bake or do a
post-masking bake... did they mask warm or hot boards trying to save
time...

Have the operators walk you through it, collect all the materials, check
all the other materials in the area. Make sure that you tell the
operators that you are not looking for somebody to pin this on, but you
need to fix the problem. You NEED their help, their ideas, suggestions,
etc...
Also let them know that if they did make a mistake, to tell you, so you
can report back to management that an error was acknowledged, corrected,
and will not happen again. Also remind the operators that when something
goes wrong (like a supervisor telling them to violate procedure to save
time) that they should notify the process engineer ASAP to reduce the
damage. My favorite reason for computer controlled processes is the
reduction of supervisor influence on my processes!!

I repeat, do the walkthrough... its amazing what you will learn.

Steve Mikell
[log in to unmask]  


  ----- Original Message -----
  From: "Steve Gregory"
  To: [log in to unmask]
  Subject: Re: [TN] Humiseal Masking Tape Residues/latex peelable
  Date: Fri, 2 Feb 2007 14:18:31 -0600


  Hi Michael!

  Believe it or not, it is adhesive. When we go to remove the residue,
  it's real gummy and sticky...just like the tape adhesive. Take a look
  at
  this picture:

  http://stevezeva.homestead.com/files/Tape_Adhesive.jpg

  It's a piece of the tape that I've taken and carefully scrapped at on
  the sticky (adhesive) side until I've gotten to the carrier part of
  the
  tape, and the carrier part of the tape is actually clear...it's the
  adhesive that's tan. I looked at the MSDS and the tape is actually a
  polyethyleneterephthalate film, and the adhesive is listed as a
  rubber
  adhesive.

  Like I said, I've never had this problem before.I used Humiseal tape
  over at LaBarge while I was there, and switched our conformal coat
  area
  over to the tape since I've been here at OAI. I've just now started
  seeing the problem.

  The tape doesn't stay on the board for more than 1-hour after
  spraying
  before we remove it. The one weird thing that I am seeing is that I
  only
  see the residues at places like in my first picture where we've
  masked
  over PTH locations where the tape is completely on the PCB
  soldermask. I
  don't see the residues on places where the tape is over the tin/lead
  board finish, or metal (like the connector sheilds on press-fit
  connectors.

  -Steve Gregory-




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