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December 2012

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Subject:
From:
"Kenneth J. Wood" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Kenneth J. Wood
Date:
Tue, 11 Dec 2012 08:18:43 -0500
Content-Type:
text/plain
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text/plain (212 lines)
The units are not airtight and some small amount of moisture is inevitable /
acceptable.
The linx guys got back to me and said that they use Zytel HTNFR52G30
Polyimide for thier lids.
Any thoughts?
Ken


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
Sent: Monday, December 10, 2012 7:20 PM
To: [log in to unmask]
Subject: Re: [TN] Polymer Lid

Ken,

Also consider that if you seek to create an enclosed cavity, the air inside
that cavity will expand during heating and sometimes create blow holes in
the 'seal' during heat cure of the adhesive.  Similarly, during reflow,
depending upon the adhesive used, you can 'pop' the lids off.

I've encountered situations in the past where a small hole was left in the
lid to avoid the 'over pressurization scenario' and then 'sealed'
post-reflow.

Can you use a deep drawn metal lid as opposed to a folded type metal
lid/shield?

You could use a logo on sticker to cover the vent hole afterwards...


Steve Creswick
Sr Associate - Balanced Enterprise Solutions
http://www.linkedin.com/in/stevencreswick
                         616 834 1883






-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kenneth J. Wood
Sent: Monday, December 10, 2012 6:58 PM
To: [log in to unmask]
Subject: Re: [TN] Polymer Lid

Bob,
I'm using a metal lid for the larger size modules now and it is a pain to
say the least to solder them on manually.
One of the issues in the past was liquids getting under the lid during
cleaning.
That's why I wanted a plastic lid with no seams that could be filled with
goo and glued down.

These units are supplied as a module to end uses so they have to have the
lids on from us.

Ken

-----Original Message-----
From: Robert Kondner [mailto:[log in to unmask]]
Sent: Monday, December 10, 2012 6:48 PM
To: 'TechNet E-Mail Forum'; 'Kenneth J. Wood'
Subject: RE: [TN] Polymer Lid

Kenneth,

  Yes, I looked at your link so now I see better. Your users will be doing a
reflow.

 So you need a thermoset lid. Glue it on with a silicon and I think you are
set except maybe for cleaning.

 I would imagine your customer will clean their boards which would tend to
trap fluids under the lids. So then you get into the area of filling and
sealing? That is a mess. It gets worse as you have SMT leads coming off the
PCB. If you can place filling holes in the PCB you can get the right amount
of material in the unit except for the filling of voids. I played with this
once and using a vacuum fixture to removed voids can cause a mess. You need
to vacuum then fill with the vacuum applied. Then reintroducing air fills
voids as air pushed down through the fill holes.

A mess to fixture. 

You might look at cavist.com as they do low temp thermoplastics, maybe they
can do a low temp thermoset so you can encapsulate soldered modules. 

Or consider metal cans? :-) 

 Getting the right amount of fill material to provide a filled sealed device
is very difficult. 

Bob K.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kenneth J. Wood
Sent: Monday, December 10, 2012 6:04 PM
To: [log in to unmask]
Subject: Re: [TN] Polymer Lid

Bob,
Thanks for your help on this.
Quantities are 1,000 to 50,000 per year and the lid needs to be glued on
before it ships to the end users.

Ken



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Monday, December 10, 2012 5:58 PM
To: [log in to unmask]
Subject: Re: [TN] Polymer Lid

Kenneth,

 I looked into this some years back and any material that "Stands Up" to
reflow temps would be difficult to form. Injection molding would probably be
impossible but ask, don't take my word.

 At all costs is there any way to add it as a last step addition to a
finished PCB?

 How many are you talking about?

 I did have some plastic parts made from a thermoset. It was black material
and I forgot the trade name. It was probably just a phenolic material. Not
sure how well it takes reflow temps. If you need help contact me off line, I
will get you a sample. I had some 2 x 4 inch boxes and cover made.

Bob K. 






-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kenneth J. Wood
Sent: Monday, December 10, 2012 5:30 PM
To: [log in to unmask]
Subject: [TN] Polymer Lid

Hi all,
I need to design a polymer lid that gets glued on top of a square PCB.
The lid will be 0.66" x 0.66" by 0.20" (maybe 0.025" wall thickness) with a
flat top so I can have the company logo and part number printed on it.
The PCB itself is a system that gets soldered to a main board by way of
castellated holes.

My question is, what lid material should I use since this unit must go
through a reflow over?

I assume a vacuum formed CPVC lid would melt right?


The unit is somewhat similar in mechanical characteristics to a Linx module
like the TXM-xxx-es

https://www.linxtechnologies.com/resources/data-guides/txm-xxx-es.pdf



Thanks
Ken


_____________________________________
Kenneth J. Wood
Saturn PCB Design, Inc.              
[log in to unmask]
www.saturnpcb.com



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