OT: board mount SMA connector

Sigma · Joined: 03 May 2004 Posts: 48 Location: Sg

Hi, all,
Normally how is the board mount SMA connector sit on the PCB?
Using glue or soldering?
The SMA connector i am referring to is like CONREVSMA002 (right angle) in the attached link.
http://www.linxtechnologies.com/index.php?section=products&category=connectors&subcategory=rpsma
Thanks.
Sigma

Ttelmah · Guest

Soldered.
The body pins, make the electrical connection, as well as provding the mechanical support. If the product is going into an enviroment with high vibration/mechanical stressed, consider potting, or using a cable attached connector instead.
The manufacturers will normally publish a drill pattern detail for the connector, and it is particularly important to have the hole sizes reasonably accurate.

Best Wishes

Sigma · Joined: 03 May 2004 Posts: 48 Location: Sg

Thanks. Ttelmah.
The vendor did provide detailed hole drawing. Thet recommend using 5 same size non plated through holes. That's why i was wondering whether to solder the center (signal) pin, then glue the four others.
regards
Sigma

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

Getting a good electrical connection on the outer pins is as important as the inner pin. At real low frequencies you may get away with only one ground pin, but it costs so little extra to do it right. If you are going to solder the board it is easy to just solder everything. Electrically conductive glues are a last desperate measure.
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newguy · Joined: 24 Jun 2004 Posts: 1907

I'd ask the vendor again if they really meant that the 4 outer ground conductor holes are supposed to be non-plated through hole. That sure doesn't sound right.

It's been a while since I've done anything with those types of connectors on a board, but I remember them as requiring plated through hole for the center conductor and for the 4 ground pins.

Sigma · Joined: 03 May 2004 Posts: 48 Location: Sg

Thanks, all.
The frequency range i am dealing with is 433mhz. Previous i am using a quarter wave length wire as an antenna. It works fine.
Now i think i can just replace this wire with a proper antenna with the sma connector.
Do i need to ground the outer pins of the sma connector? Last time i thought i need not because the inner connection already acts as the quarter wave length antenna and the outer pins are just as the supporting pins.
Anyway, i have already send inquiry to the vendor already.

regards
Sigma

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

If the antenna is just a 1/4 wave whip you don't need the ground pins electircally, though they should be strong mechanically. But if the antenna is any sort of coaxial, folded dipole, or gamma matched rig it will use the ground line too.
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Ttelmah · Guest

I suspect two possibilities arise.
The first is that you must remember that PTH, has a significant tolerance, and tends to result in holes that are not quite parallel sided. It _may_ potentially be stronger to have a drilled hole, that is almost an interference fit to the legs, than a PTH hole that is oversized, and only touches in the very centre of the board. However if your board company has good working accuracies, I think this is unlikely.
The other possibility, relates to the thermal behaviour of the pads and legs. There is a significant amount of metal in the plug, and when having boards wave soldered, the manufacturer I used, recommended applying resist filler to the holes for this type of plug, and then having these manually soldered afterwards, since he could not guarantee good through wetting with the wave soldering process. This may reflect the reason why non-PTH is being suggested.

Best Wishes

Sigma · Joined: 03 May 2004 Posts: 48 Location: Sg

Thanks for your advice.
The vendor said they should be five PTH, which made me even blur.
Please refer to www.connectorcity.com/documents/conrevsma002.pdf
If they are PTH, what should be the proper dimension for the diameters and the holes? The pdf attached only indicates 5 60mil holes. Confused. Mad

Thanks.
Sigma

Ttelmah · Guest

This is again down to talking to your manufacturer. In most cases, you can specify the finished hole size, and your board maker, will apply the correct adjustments. The problem is that the allowance for plating, will depend on the plating thickness being used, the board thickness, and the hole size (plating tends to be slightly thicker in larger holes). This is why most people specifying boards, will take advantage of their manufacturers 'knowledge' to get this figure correct. People working via some automated PCB services, instead have to specify the 'drill' size, rather than the finished size, and hope that the allowance is right...

Best Wishes

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Sigma · Joined: 03 May 2004 Posts: 48 Location: Sg

Thanks, PCM programmer & Ttelmah,
I know how to define the dimension of via. I am just wondering how to define the proper dimension so that they will have minimum interference when operating at RF frequency.
Thanks.
Sigma

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

At 433MHz a quarter wave is about 6.5". Any dimension under an inch is going to be "short" by RF standards. The RF dosen't care what the dimensions of the via are as long as there is enough copper to carry the current, enough gap to hold off the voltage, and enough mechanical strength to hold everything together.

There is nothing magical about RF.
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