Stephen,
I found a similar part on the ANAREN site that has a data sheet with a
recommended footprint and mounting considerations...
Their Xinger product line shows a lot of vias under the part. It appears
that the actual board that you are working with has more vias in it than the
recommended footprint shows. In my opinion, the vias are too close to the
edge of the footprint and will suck the solderpaste into them when reflowed.
You may be able to compensate by using more paste but that usually doesn't
work very well and has other potential problems with it... In reality, the
fillet on the edges does nothing more than let inspection know a good solder
joint was achieved, and lends little to the performance of the directional
coupler... the main thing is getting a good low impedance ground to the
coupler so it will function as advertised... The designer could redo the
footprint to use a pattern of vias similar to the footprint showed in the
data sheet link below, and use as small a diameter via as possible without
running up the cost of manufacture to impede the thieving of the solder to
the vias under the part... RF parts always have weird requirements to work
properly... I worked at REMEC in San Diego for a number of years and they
did things like this all the time...
http://www.anaren.com/pdfs/1D1304-05.pdf
Another though that occurred to me is you might be able to mask the vias
from the far side to prevent too much wicking of the solder with the current
design and apply some flux to the exposed copper edges prior to reflow and
see if that helps with the job as is...
Make sure to discuss the issues with the designer of the board and the RF
engineer. Typically the middle man (purch, QA, etc..) doesn't really know
what can and can't be done... he/she just goes by whatever the print
says....(which is not necessarily up to snuff to communicate the design
intent)
Good luck,
Bill Brooks
Senior PCB Designer - [log in to unmask]
Zoneworx, Inc.
40925 County Center Drive, STE 200
Temecula, CA 92591
http://www.zoneworx.com
Tel: (909) 296-1226 x 1037
Co-Director / Education Officer / Webmaster
for the San Diego Chapter of the IPC Designers Council
http://www.ipc.org/SanDiego/index.html
http://home.fda.net/bbrooks/pca/
-----Original Message-----
From: Stephen R. Gregory [mailto:[log in to unmask]]
Sent: Tuesday, August 29, 2000 12:33 PM
To: [log in to unmask]
Subject: Re: [TN] Castellated Hybrid soldering...Pic's are up
In a message dated 08/29/2000 1:16:08 PM Central Daylight Time,
[log in to unmask] writes:
> Well, I have seen some interesting problems before... I wonder if you
could
> show us a component mounted to give us an idea of what the customer is
> objecting to...
> I have solved some of these problems using "solder dams", a thin line of
> soldermask to prevent solder thieving from the close vias...
> It would help though to see what the actual problem is... it's hard to
> visualize.
>
> Bill Brooks
Hi Bill!!
Picture is up, it's called Hybrid.jpg...go to:
http://www.driveway.com/share?sid=e25a88c4.8e904&name=Pictures
What is being objected to is that there is little, or no solder fillet where
I've indicated in the picture. The RF castellations are filleted, and there
is a teeny fillet in the ground castellation, but no filleting along the
horizontal edges on the ground pad.
The part is placed on top of solderpaste (you can see the paste print in the
other picture here), and the bottom of the component body is soldered
directly on the gounding pad. But with all the via's and the exposed copper
along the edges, there's not a snowballs chance I'll ever get decent fillets
where they say they want them.
I can hand add them for a price, but I don't think it should be
necessary...but hey, I'm not an RF guy...
-Steve Gregory-
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