Hey Ingemar,
I agree with alot of what has been said and it is very good information, but what I was curious about was the materials used. One of the statements mentioned was whether the solvent base was considered a "fast" or "slow" solvent - this makes a huge difference depending on the application method utilized as well as the coating type. We are currently using an inline 8 gun selection conveyorized spray system spraying acrylic Humiseal 1B31-LOC with what I consider a "slow" solvent applicator. In the past we have had issues with the mixture ratio's (viscosity) in which not enough thinner was added to the mix and thus causes the "webbing" defects to literally fill the booth within about 3-4 minutes. We also had an issue when an operator used IPA instead of the thinner and this caused the booth to fill in about 20-30 seconds. So you may want to look at and make sure you are using the correct thinner additive and make sure there was not a mistake. There was also a statement about pre-baking the CCA's prior to coating them - with my experience if they are coated while the CCA's are still hot, then you may see the defects mentioned and others.
I would just go through the entire process variables and make sure they are in fact set correctly. Change out the chemistry, purge the coating lines (if possible), check the temperature (69-73 should work just fine), make sure the atomization is correctly set and that the air lines are free from moisture, make sure the CCA's are actually clean prior to spraying them (this is a very big deal and needs to be validated or it will causes many problems), and last but not least as mentioned check the coating container to ensure that it has not been exposed to the environment for over 24 hours (as this will cause the base solvent to evaporate and change viscosity). Oh and one last thing. Check the output volume of the guns to ensure that they are within the set band. If you have a low out level and a high atomization setting, this may cause you problems as well because depending on the viscosity of the material will produce a very thin and weby type appearance on the CCA's substrate.
There's my 2.5 cents
Good Luck
CAS
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Ingemar Hernefjord
Sent: Thursday, October 27, 2005 9:32 AM
To: [log in to unmask]
Subject: [TN] Urgent! Acrylic coating
Hi all,
I got a call from our production. They stopped the board coating. All
boards get white and superthin veils, patterned like fractals or roses.
I'm at home because of illness, so I can't participate in their work
with the problem.
I asked them for how long they bake the board before spraying, and they
told me that no baking is made at all. Does sound wrong to me. My first
theory is humidity in some form. Humiseal, don't have the article number
just now.
Anyone who has a tip?
I'll get pics sooner, maybe I can resize them for Steve's gallery.
Thanks in advance
Ingemar Hernefjord
Ericsson Microwave Systems
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
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 1.8e
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
-----------------------------------------------------
|
