EMI shielding soldered by reflow - possible?
I am designing a microwave transceiver and I want to add a metal frame for RF shielding. Problem is a have little experience with manufacturing... The frame is to lie all around the transceiver area on the PCB, for which I will provide a large rectangular PCB trace on top layer connected with lots of vias to the ground plane. Connections with the circuits outside are being done with traces in the two bottom layer (it is a 4 copper layer stack) and vias.
- Question A: Is it possible to solder the metal frame at the same time as every other components by solder reflow?
- Question B: How to make a reliable stencil for solder paste deposition? The shielding frame should be solder all around, but if I make such a cut in the stencil I would get a detached rectangle inside...
Help, please? :)
Anyone, please? :)
http://www.leadertechinc.com/
Yes, I know that supplier, but my question (how to design a proper footprint for a stencil and for solder reflow) remains unanswered.
Yes, I checked the PDFs throughly. :)
Does your shield have PC pins like the ones linked above, or it it surface mount all the way around? If the latter, then I would leave some thin bridges across the shield footprint on the stencil (how thin and how many is hard to know, depends on the stencil material and method of paste application). You should be able to get ~80-90% coverage of the pad area, and surface tension in the solder should cause it to distribute itself evenly during reflow. Hopefully there will be enough solder overall for a good joint.
Yes, this is my problem. Do you know where I can get some "rules of thumb"/"good practicies" for these?
Leader tech is just one of many companies. But if you look at their data sheets, you will see some two part shields: a cover, and a surface mount corral. You pick the L x W for one of their standard sizes, and the solder pads needed for it become obvious.
Later after the corral is soldered on, you just snap the top cover into it.
The only trick is if you need to get RF in and out of the corral. Use a thick solder mask there. Or you can go down to an internal metal layer if it is a multilayer board.
Not that simple, I'm afraid. :(
For effective shielding one can not just stick with the solder pins. Usually these are too far away appart, so you get a bunch of radiating slots between the PCB and the corral. At least, one must stick with a spacing between solder points well below the wavelength, say 1/20. The best solution is to solder all around (no slot whatsoever). This is my problem: how to do a stencil that allows me to solder the corral all around. I think I explained it better now. :)