SMD daughter board mounting

1] Hard to inspect (like QFN parts)

2] Are you going to glue the parts down to the module so they don't come off during the second soldering operation?

3] Are you allowing vias on the lower surface? If so you need to tell the customer to use a keepout on the upper layer. Maybe there are thermal pads too that have to be soldered.

Best regards, Spehro Pefhany

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You could put pads on the bottom and mount it BGA-style, like a Linear Tech LTM-series module.

Or do this:

That's just normal PTHs that are routed through. Works great.

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

What does the gerber look like ??

How do you do this in your CAD software ?

Does the board shop charge more for this ?

thanks

Am 04.06.2012 05:53, schrieb John Larkin:

We use the same style to mount plastic Virtex FPGAs in places that later will be inhabited by mechanically larger, outrageously priced hermetic flatpacks. It works. :-)

Gerhard

On a sunny day (Mon, 04 Jun 2012 11:11:37 +0200) it happened Gerhard Hoffmann wrote in :

I test those little modules like this:

This is a module from ebay, altitude, pressure, temperature and compass, has a PIC 16F689 to do the math from the sensors.

To test and caibrate the compass I had to wave it around, for that mounted the module in a SD card box:

Whole thing interfaced via 3.3V PC par port with iic bus, power also from a parport data pin, 1 mA. There are some diodes in that connector shell, sda pull down, scl pull down. Works great Later it can be soldered somewhere in ze Spazekraft. :-)

Neat! Is it routed after the plating? I would have worried about the mill ripping out the plating in the holes.

George H.

.highlandtechnology.com=A0 jlarkin at highlandtechnology dot com

snipped-for-privacy@yahoo.com schrieb:

Hello,

if soldering by hand should be possible too, you should place the pads not only on the bottom layer, but also at the edges of the daughter board. Your pcb maufacturer should plate not only the holes but also the edges above a pad.

Bye

Just round pads.

I think we used eight of our regular TPs, test points, which are just PTHs.

Not for routing halfway through the pads. There was a lot charge for panelizing and such. They solder coated and hot-air leveled after routing, which sort of filled the half-moons with solder.

Sure. This was a hack to replace a few thousand MAX9690 comparators that were going flakey on us in the NIF timing system, controlling roughly $6 billion worth of laser.

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

It's solder coated and hot-air leveled after routing.

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

So you have a PCB edge running thru the pads ??

How does the board shop know whats to be done ??

Special instructions ?

Is it self obvious ??

What do I tell the board shop to expect to have to route thru the holes ??

I have been looking at how to get a board shop to do this, but I don't know what I need to do in my CAD software.

Thank you again

Here's the fab drawing. We talked to the PCB house about the panelizing and such, but I guess we could have gone into more detail on the fab drawing itself.

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

A technique I've used a decade+ ago is placing pads with through holes on the edge of the pcb. When the board is routed, you have half a pad left which you can use as a surface mount pad. Easy to inspect and hand solder. I see this used on Trimble GPS receiver modules (look up the 77766 for an example). Cleaning the board may introduce trapped flux under the board.

gps,wifi,bluetooth

I've also seen GSM

-Lasse

Yes. "Concave" pads on the edge like some resistor arrays might be an idea. After some thought we're going to stick with thru-hole pin mounting for this spin, but it's still an interesting notion.

Yes. Although they should just re-flow in place, held by surface tension, right?

to

ybe

I've got some VXO modules that are tiny SMD PCBs with pads on the bottom--I'll have to dig and see what they did.

If we did this in the future we'd have a ground pour on the bottom, which might require either blind vias, or routing everything on the top.

Thanks!

-- Cheers, James Arthur

That was the first idea.

Darn. I thought I'd thought of that. But hey, at least it works!

Thanks.

-- Cheers, James Arthur

t e

Well, this gadget has an antenna, so I'm thinking we'll need to enforce a certain spacing off the motherboard. This time, that means pins. For that reason I don't think SMD of the module works this time, but the idea might be useful elsewhere.

Placing a row of feedthrus and routing off half to leave concave 3-D pads (as John said) would make the thing easier to inspect too.

I've hand-soldered pads underneath a part, that came all the way to the edge. It wasn't hard. But the concave pad would be easier still.

Thanks for the thoughts.

-- Cheers, James Arthur

Good, that seems to be the consensus, and it's heartening to see several people have done it.

Small bumps or something might enforce a gap to the motherboard for cleaning, like with ICs. It still might not come clean for a board this big. Seem okay for Lasse's modules (below). Hmmm.

Useful. Thanks.

-- Cheers, James Arthur

t e

Good data points. Thanks. Nice modules too.

-- Cheers, James Arthur