board to board surface mount

[zappedagain]

I have an application where I need to convert the surface mount footprint (pads) of one device (similar to N-SOIC) to an existing board layout for another device (also similar to N-SOIC, but different spacing and number of pads). I'm picturing having the device mounted on a small PCB, and then soldering this PCB to the footprint on the existing board. I've seen this type of thing for thru-hole. Does anyone know of any options for surface mount devices?

I'm picturing a small C-clip that would clip over top and bottom side edge contacts on the adapter board. The spring force would hold it on the board, or it could be soldered to the top side. The bottom side would then look like a J-lead (gull wing) contact to mount on the bottom board. Does such a thing exist?

Another option might be to have vias placed so that they get milled through when the board outline is milled. This will leave a solderable surface on the 'edge' of the PCB between the top and bottom layers that could then be soldered to the bottom PCB. Has anyone tried this? I worry that the milling process might damage some vias. It seems this could be detected via a visual inspection before the adapter boards are used.

 

[itsmoked]

ugah ugah my head hurts now.

Zapped; SHOW us the board IC footprint. This can be the original IC footprint/pinout. And then show us the new IC footprint/pinout.

Then we can give you a solid bunch of suggestions and ideas.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[zappedagain]

Hmm, I don't have plots or photos handy. The pads are 0.7mm x 1.8mm on 1.27mm spacing on the component and the board; the component wants the same pads.

I have a bit of room to bend the pins to a narrower spacing (the board is about 22mm, I can probably bend the component leads to about 18mm). The component is a fiber optic module.

I expect I'll need to do this with blind vias, or maybe buried vias.

I did talk to a board house about my second option and they said they have done this type of thing before. It works better with larger vias; unfortunately with 1.27mm spacing I'm probably looking at 0.5mm holes maximum after all the tolerances add up. They did say that a lower aspect ratio helps (board thickness / hole diameter) so I might try this on a 0.81mm board if I can still get blind vias.

 

[zappedagain]

Well, it looks like both ideas are valid. A colleague found that Mini-Circuits is using the clip idea. See:

http://www.minicircuits.com/products/imps_main.html

for a photo. The actual part is ALMP-5075 if they change the site. I'm not sure if the leads are custom made for MC or if they are available off the shelf.

And CEL is using the via as a pad idea. You can see it at:

http://www.cel.com/product.do?command=viewOverview&group=5&source=_home

on their FreeStar ZFSM-100 and a few other models. They didn't do it to the tight spacing I need but it proves out the concept.


Anyway, all this is just for closure. We decided to drop the project and make a new module that is compatible with the PCB footprint. Happy New Year!

 

[itsmoked]

LOL Thanks for the 'closure'.

BTW: Often when doing some random PCB we'll tag on an adapter board like you we looking for. Then we have a selection of them laying around to use for development, or disaster remediation.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com