When you say that, Joyce, I remember a practical joke we played 30 years
ago. We were pretty good at so called 'hybrids', RF type, ceramic
substrates mounted in machined Kovar packages. We made a couple of packages
of wood and sent them to an expo in USA. On the stand's wall you could read
that this was a way to lower the costs essentially. Caused many smiles and
also serious questions. They were stolen last day, and we chuckled "
russians".  This was in the days humor was larger part of the daily work
than it is today.
Inge

On 11 December 2012 15:19, Joyce Koo <[log in to unmask]> wrote:

> Why not metal lid? With such a low volume, can't be the cost.
> --------------------------
> Sent using BlackBerry
>
>
> ----- Original Message -----
> From: Steven Creswick [mailto:[log in to unmask]]
> Sent: Tuesday, December 11, 2012 08:44 AM
> To: [log in to unmask] <[log in to unmask]>
> Subject: Re: [TN] Polymer Lid
>
> Ken,
>
> I did not mean to imply that this would create a seal to keep moisture out,
> but simply to point out that an enclosed volume of gas will expand when
> heated.  If one is not prepared for this, it can cause surprises.
>
> We did things like this in the hybrid industry over 30 years ago, using
> ceramic substrates and ceramic shells/lids.  Definitely NOT hermetic, but
> served their purpose for industrial applications.
>
> I believe that Zytel is a glass reinforced polyamide.  Not familiar with
> this particular one, but my experience with LCP's has been that they can
> offer greater temperature resistance, but likely cost more....
>
> Try it before you buy it!  Get some samples from the folks cited.
>
>
> Steve Creswick
> Sr Associate - Balanced Enterprise Solutions
> http://www.linkedin.com/in/stevencreswick
>                          616 834 1883
>
>
>
> -----Original Message-----
> From: Kenneth J. Wood [mailto:[log in to unmask]]
> Sent: Tuesday, December 11, 2012 8:19 AM
> To: 'TechNet E-Mail Forum'; 'Steven Creswick'
> Subject: RE: [TN] Polymer Lid
>
> 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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