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May 2008

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Subject:
From:
Hernefjord Ingemar <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Hernefjord Ingemar <[log in to unmask]>
Date:
Thu, 29 May 2008 13:49:59 +0200
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Mr Trikeman,

 .... and the answer is ..fused center pin...fused thickfilm...

Your proposal fits exactly with my theory.  The center pin is not any
more. Vaporized. This coax transferred RF power to an antenna. A number
of 3,000 dollar hybrids are now useless. I will make a report for the
substrate manufacturer and ask him to go back to center oriented vias.

Thanks, may the winds be with you..

Inge

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Creswick, Steven
Sent: den 29 maj 2008 12:16
To: [log in to unmask]
Subject: Re: [TN] via placement in LTCC

Ingemar,

Good afternoon!

Depending upon the robustness of the solder fillet, I can visualize a
problem with the circumference of the pad/s lifting/peeling during temp
cycles.  Large, heavy, robust solder fillets leading to eventual open or
intermittent circuits.  Whereas light, delicate, thin fillets survive
nicely.  

In my minds-eye, I picture the perimeter as being a relatively high
stress area and not an exceptionally good place to put an interconnect
via - keep it in the center/neutral stress point.  Adding a protuberance
to the perimeter would seem like adding insult to injury.

Back in the olden days of conventional thick films, we would actually
put down a ring of dielectric around the edge of a circular pad such as
this to 'help hold it down'.  Assuming the solderable conductor is
co-fired in your case, that would seemingly be of negligible benefit.

You are being a little tight-lipped about the problem observed, but I
bet that you are seeing pad lifting at the edges.

.... drum roll ......

   



Have a good day!

:-)  Steve

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: Thursday, May 29, 2008 5:59 AM
To: [log in to unmask]
Subject: [TN] via placement in LTCC

 
Mr Trikeman or someone else with one foot in LTCC, need advice.

Imagine a 90 degree SMA coax connector for solder mounting on LTCC
silver thickfilm pads.
The RF connector center pin is soldered to a circular thickfilm pad,
that is double the diameter of the  RF connector center pin.

Now, these pads communicate by means of vias in the blue tape (the
dielectric). First, the vias were placed in the center of the circular
thickfilm pad, later, someone decided to move the via to the periphery,
i.e. off center. The designer has added a small land (ear)to the
circular thickfilm pad, and it's here the vias are removed.

The later design has caused some trouble. Seems as the off-center via
placement wasn't good.
I got some ideas what it's all about, but first I would like to hear
with  you, guys

Hope my description is understandable.

Inge 

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