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Experience with surface-mount SMA jacks?

I've got a crosstalk-sensitive application that could benefit from jacks like these:

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... but I've never used them before, and have never seen anyone else use them either. I like the idea of a planar footprint with no center or ground vias, but it just seems like asking for trouble when the mating connector is torqued.

Here's what bugs me: assume the center pin is free to rotate so it doesn't contribute anything to the polar moment of inertia. That leaves the four ground pads. Their soldered area is about

10 mm^2 (i.e., 4 x 1.6mm x 1.6mm), centered on a 3.5 mm radius. An SMA torque wrench (like anyone ever uses those) will break over at about one n-m, which corresponds to a force of 15 n/mm^2 at that distance. Meanwhile, the shear strength of a solder joint under various conditions ranges from about 14 to 27 n/mm*2 according to
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.

Is my math busted, or is that a nonexistent safety margin? Maybe I shouldn't treat the ground pads as points on a circle?

-- john, KE5FX

Reply to
John Miles, KE5FX
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Dead link (just brings me to their catalog listing). Was that like a one of these..?

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(DK links are weird.. even if I hit the "share " button, I'm not really sure if it's going to work correctly or not...)

Feels right to me, just from a hand-wave about how I'd feel putting a wrench to an SMT (I mean, *really*?!).

Has to be vertical, not edge-launch?

You can *mayyyybe* get lucky with finding a kind that's got real ground pins, and has an SMT center contact (without being an edge-launch as such), but... seems real unlikely?

Ah.. the same style as above, but with long pins, does exist...

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...but good luck touching it up with the soldering iron, if you need to.

There's a style of connector where the tubular body extends back onto the board, then opens up to reveal the center pin (which can be accessed with an iron from the top side), and the ground pins sit around the opening. It would be neat if they made that kind with a gull wing center pin, so you can solder it SMT, and still hand solder it.

Otherwise, there are tons of pure-SMT connectors, with press-lock styles -- Ultramini (and U.FL, and etc.) is like a very, very small SMB. I wouldn't trust 'em for more than about.... one insertion?

Oh hey...

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here's a thing that exists. Not that it's cheap though, and what the heck is SMP, who uses that. Irony now is that it's press-lock, not threaded, so you don't /need/ excruciating torque on the poor thing...

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: http://seventransistorlabs.com
Reply to
Tim Williams

Got a more specific link?

We use these edge-launch SMAs:

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and they work great. We did a bunch of em simulation with ATLC to get the layer stackup right for the best launch match.

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It TDRs very nicely.

That connector is from Shining Star, costs $1.78.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics
Reply to
John Larkin

Sorry, yes, the one Tim cited is what I meant. There are several manufacturers with similar parts.

I like the edge-launch parts as well, but they're a bit pricier (or a LOT pricier) and take up more room than the SMT jobs.

I wish I could use Chinese vendors, but somebody always wants to see a RoHS material declaration, and nothing makes the Chinese clam up like asking for a material declaration.

-- john, KE5FX

Reply to
John Miles, KE5FX

Edge launch is my second choice, nothing wrong with it but it'll take up more space.

Just gotta use a bigger iron. :-P That one is interesting, but it's safe to say the assembly house has never seen anything like it. Hmm.

I've been using a lot of JSC jacks on test boards, but I need double shielding and good phase stability for this particular task, so no press- fit stuff.

SMPs are nice, sort of a big brother to MCX. They've been around a while. I don't think many people besides the military and other high-end customers ever used them, though, so they're overpriced.

-- john

Reply to
John Miles, KE5FX

We use lots of the 5-pin right-angle thru-hole parts too, SMA and SMB. They are not a good a wideband impedance match as the edge-launch ones.

Like this:

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They work fine, no mechanical problems.

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--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics
Reply to
John Larkin

FWIW I've used these SM SMA's in a design and had no problems when torquing to 8 lbft. These connections were internal to the unit, and only needed to be made at the factory. If you're considering them for a user accessible connector then it would be prudent to conduct some tests.

Reply to
JM

I use a fair number of SMT MMCX edge-launch connectors, which meet that description. They solder all along the length of the connector, so they're pretty durable.

Otherwise, it's through-hole all the way for me, and all bulkhead-mount, through-hole, die-cast metal BNCs for anything involving students. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

A surfmount right-angle SMA would need some serious number of vias to keep the pads from being ripped off the board. And it's still scary.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

Yup. I like the MMCX ones because the cables are super skinny, so that in a fight between cable and PCB pads, the cable will very likely lose. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

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