Hi George,
FYI, we do #2. Gigalink in Holland make suitable coax conns with
pins for stripline interfaces. The center pin is formed like the stripline
itself. Expensive, yes, but cheap solution compared to what we did
earlier. Sending pic offline. Thx for sharing your experience.
Ingemar Hernefjord
Ericsson Microwave Systems
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Wenger, George M.
Sent: den 17 december 2004 22:17
To: [log in to unmask]
Subject: Re: [TN] Wanted: TN's best-on-coax-soldering
Bill,
After looking at the photograph it appears your guess was correct. It
certainly does look like a thermal-fatigue induced cohesive solder joint
failure. In the high power RF world where you need to get rid of a lot
of heat you see lots of opportunities for these kinds of solder joint
failures. We've gone through four ways of preventing them:
1. Eliminate the CTE mismatch which is not practical most of the time.
2. Increase the integrity/robustness of the solder joint by making the
soldered length longer and the solder joint thicker. This helps most of
the time because it extends the solder joint life but it doesn't prevent
the fatigue.
3. Stop the excursion by fastening the board to the chassis to reduce
the CTE mismatch induced excursion. Our trials with adding screws is
only marginal because the board usually slips under the screw head. The
preferred mechanism is to pin the board near the solder joint.
4. But as bill indicated the best way by far is to add compliancy so
the excursion doesn't fatigue the solder joint. Adding a ribbon or
changing the shape of the interconnection lead to a gull wing are just
some of the ways to add compliancy.
Our design rules call for doing a combination of #2 and #4 as well as
asking our designers to keep in mind the location of these types of
solder joints so we don't have to do #3.
Regards,
George
George M. Wenger, Andrew Corporation
Reliability / FMA Engineer
Base Station & Subsystems Group
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brooks,Bill
Sent: Friday, December 17, 2004 3:50 PM
To: [log in to unmask]
Subject: Re: [TN] Wanted: TN's best-on-coax-soldering
Hi Steve,
Very interesting photo, do you have more from different perspectives?
The soldermask 'dam' is a great example of a technique I used at another
company.
The 'coined' or flattened lead from the SMA looks to be pulled away from
the
solder joint... I would guess this happened after a thermal excursion,
where
the chassis expanded faster than the board and the lead literally pulled
the
SMA pin loose from the solder connection.
I can't tell a lot from the photo because of the frosted Plexiglas
appearance surrounding the top of the photo, but I have see this sort of
failure before in similar situations...
The solution to the problem is to strain relief the connection.
We used a silver ribbon and soldered it to the pin and the board
allowing it
to flex to take up the CTE mismatch between the aluminum housing and the
Duroid board.
Hope that helps... let me know if I read the problem correctly... it was
just a guess based on what it looks like to me from here... not being
able
to see the whole picture...
Best regards,
Bill Brooks - KG6VVP
PCB Design Engineer , C.I.D.+, C.I.I.
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
e-mail:[log in to unmask]
http://www.dtwc.com
http://pcbwizards.com
-----Original Message-----
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Friday, December 17, 2004 12:35 PM
To: [log in to unmask]
Subject: Re: [TN] Wanted: TN's best-on-coax-soldering
Sorry Everyone! My bad, I didn't have the thumbnail linked to the
picture...but it is now. Try this link:
http://www.stevezeva.homestead.com/files/SMA.jpg
Just got in a hurry when I posted the picture. I'm trying to get all my
loose ends tied-up here at work because I'm leaving this weekend for
Christmas vacation.
-Steve Gregory-
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