Hi Glenn
've been exactly that path = because of relatively (to solders)
insufficient strength of polymers the mid anchor helps ;
agree ; obviously something forces you to epoxies .
Therefore :
1
The dispensing in one pass should be easy if you have at least dual pump
head , one for con , one for non .
If you don't have dispenser yet ; go for camelot's 642 head .
2
One cure range in one pass again is no problem , if you'll get a problem
to locate all the suppliers ( grace; ablestick, loctite , ciba, dexter,
etc. contact me off line .
3
The idea of having a punch cake underneath = 3 horizontal layers I don't
really fancy as you'll most likely get into SIR problems = the
insulation will quite likely suffer, especially under humid &/or dusty
conditions ; but you may be right still .
If you can avoid contact by say dispensing dual small dot in the middle
(with single dual needle to speed it up) instead of spreading blob and
consequently you can use the same parallel spread control on pads :
Control your travel as well = not over the mid section if the stringing
is on the edge ;
with right layout you pick up a lot of speed with zero risk .
[:] : [:]
v v
I hear your dam theory ; sounds clean enough if you control it , after
all FR4 is nothing but epoxy , but I would do SIR test samples prior
just to simulate the life a little bit .
See you
Paul Klasek
http://www.resmed.com
PS
If any of you C.O.P.S. folks would like a free software = rectification
of the optimizing function ; let me know ;
I did try to post the clip on Net but it was too big to get through =
direct mail only .
> ----------
> From: glenn pelkey[SMTP:[log in to unmask]]
> Sent: Thursday, 17 September 1998 3:09
> To: [log in to unmask]
> Subject: [TN] Assy: Cocure conductive and nonconductive epoxies
>
> Hi Technetters,
>
> Does anyone have experience with cocuring conductive and
> nonconductive
> epoxies? We're looking at a process of dispensing nonconductive epoxy
> to secure the middle of a cap, then dispensing conductive epoxy for
> the
> terminations, placing the component, and then doing only one cure?
> The
> two epoxies will most likely come into contact with each during the
> dispense or cure step.
>
> We're trying to accomplish two things; additional strength of
> the
> attachment and a dam for the conductive epoxy. For risks, we see a
> potential for the nonconductive epoxy developing a barrier between the
> cap and the substrate. There's also an issue with thermal expansion
> that I need to do the math on. But, this should be pretty straight
> forward.
>
> Any stories out there? Success or failure?
>
> Thanks in advance for any input.
>
> Glenn Pelkey
> Quality/Reliability Engineer
> Maxtek Components Corp.
> [log in to unmask]
> [log in to unmask]
>
> ______________________________________________________
> Get Your Private, Free Email at http://www.hotmail.com
>
> ################################################################
> TechNet E-Mail Forum provided as a free service by IPC using LISTSERV
> 1.8c
> ################################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with
> following text in the body:
> To subscribe: SUBSCRIBE TechNet <your full name>
> To unsubscribe: SIGNOFF TechNet
> ################################################################
> Please visit IPC's web site (http://www.ipc.org) "On-Line Services"
> section for additional information.
> For technical support contact Hugo Scaramuzza at [log in to unmask] or
> 847-509-9700 ext.312
> ################################################################
>
################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe: SUBSCRIBE TechNet <your full name>
To unsubscribe: SIGNOFF TechNet
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################
|
