Hi Steve!
 
The tape is new, and all the operators that we have in our conformal
coating area have been with the company for quite some time now and are
very familiar with the process. I've stood and stared over peoples
shoulders so much that they've felt self-conscious and think that I
think they've done something wrong, which is the last thing I want to
do. I have one senior operator that I trust as my "second set of eyes",
and he tells me that the process is being carried out as it always has
been. First a pre-bake after final cleaning, then mask, spray, wait 1/2
- 1 hour and then de-mask. The boards aren't baked with the tape on, nor
are they hot from the pre-bake, they are at room temperature when they
are masked. 
 
For the time being, I'm going to have the few areas on the assemblies
that we mask and see the residues, de-masked immediately after spraying
before the coating has a chance to cure at all, and see if that helps
the situation. I'm going to do this until I am able to try the tape that
Amol Kane recommended to me, the 3M Scotch 4737T which I am ordering
today.
 
I'll let ya'll know how it works out...
 
-Steve Gregory-
 
 

________________________________

From: Steve Mikell [mailto:[log in to unmask]] 
Sent: Monday, February 05, 2007 1:11 AM
To: TechNet E-Mail Forum; Steve Gregory
Subject: Re: [TN] Humiseal Masking Tape Residues/latex peelable


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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