Terry:
            I am somewhat familiar with the parylene coating. I went to
the maker of one type of machine for a previous company and saw how they
are being built and how they work. The boards are placed in a chamber
and a lid is place over them. On one side of the chamber there is an
input from a heater that sublimates the parylene that is in a solid form
( looks like Styrofoam pellets ). At the bottom there is the outlet that
takes the gases to a cryopump and subsequently to a rough pump. There is
a current of sublimated Parylene that goes down stream and deposits
everywhere supposedly evenly. It can not be possible due to the fact
that depending on how the boards are placed some will get more  coating
than others. I remember that the vendor recommended that when we
developed a process for a particular board, we should load the same
amount every time in the same configuration. If for some reason there
was a need for less than the capacity, we should use dummy board to
obtain the same results. I would assume that the angle to the current of
parylene and the speed of deposition would make a difference. Slow the
deposition way down and the thickness variation will be smaller but more
costly. I would not worry about the different thickness as long as the
least is still within requirements and it adhesion is good.
	Regards,
	Ramon


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Terry Quinn
Sent: Wednesday, May 30, 2007 8:46 AM
To: [log in to unmask]
Subject: [TN] Parylene coating

Does anyone in this group have experience with variations in the
appearance of parylene coating?  Our vendor is applying parylene on a
small PCB.  Most of the boards still exhibit the glossy finish of the
original board mask but we see some units that have a distinctly dull or
matte finish.  Sometimes it is limited to one end or even a corner of
the board.  The vendor reports that this reflects a slightly thicker
deposition of the parylene coating and is not a cause for concern.  Can
anyone confirm this, or are there other ideas that might explain this
condition?  Thanks for your help.

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET
Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the
posts: send e-mail to [log in to unmask]: SET Technet Digest Search the
archives of previous posts at: http://listserv.ipc.org/archives Please
visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for
additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------