Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


SMT

Views: 1901

#47499

SMT | 10 February, 2007

I just started a design where I will be placeing smt parts on both side of PCB. 50 parts on top side ranging from 0602 to SOIC8 and 4 SOIC LED's on bottom. How can I assemble with parts on both sides ? I have P&P,stensil printer, relfow and solder wave equipment. no glue dispenser. I ussually do smt P&P then reflow followed by wave solder of TH parts. One other issue, the 4 LED's cannot run through wave since they are on bottom side.

reply »

#47514

SMT | 11 February, 2007

You're correct. So, you're thinking about putting the PTH parts on the same side as the SOIC LED, making the top into the bottom, right?

reply »

jerry

#47522

SMT | 11 February, 2007

No, 50 parts on one side and 4 SOIC leds on the other. The LEDs cannot go through the wave so I need to mask them off or cover them up to protect them during the wave.

reply »

#47558

SMT | 12 February, 2007

From what I see, you have a couple of options...

1. Hand solder the secondary side LED's. This is only a good option if you're going to be at low-ish volumes. Higher volumes tend to necessitate more automation to reduce production costs. However, even at higher volumes, depending on the costs of hand-soldering, it might be the most economical solution...hand-soldering once generally costs less than extra tooling, or replacing damaged parts.

2. Selective wave solder. If you've got enough clearances on the secondary side between the pads of your SMT devices, you can buy a selective solder fixture to place the board in, and only wave solder the through-hole components. This is an excellent volume solution, if your design allows it. I'm not sure of the recommended clearances, but it's either been discussed in these forums previously, or someone out there knows them and will chime in with them.

3. Mask and wave. This has worked for me on a number of occasions. We use a liquid mask that generally provides enough protection to the parts to prevent thermal issues. This, of course, depends upon the thermal thresholds of the components. Assemble and reflow per normal; mask the secondary side components, assemble and wave through hole.

cheers ..rob

reply »

#47563

SMT | 12 February, 2007

Don't count out a wave pallet. if the led's are not an extremely tall part a pallet might be just the thing for running something like this at a higher volume.

reply »

#47570

SMT | 12 February, 2007

Blob some peelable solder mask on the LEDs. They'll hold thru wave.

reply »

#47888

SMT | 21 February, 2007

just another problem with that smt stuff. think thru hole baby!

reply »

jerry

#47889

SMT | 21 February, 2007

Thank you

reply »

oldsmtdude

#48118

SMT | 2 March, 2007

They do make smt leds that mount topside over a hole and shine down ya know. Then just kapton tape the holes and wave it.

This message was posted Add this forum to your site! Click to learn more. the Electronics Forum @

reply »


Rob

#48323

SMT | 12 March, 2007

Rohm make them & call them Backfires:

http://www.rohm.com/products/databook/led/pdf/sml-812.pdf

The only problem is on some applications you may have to use light pipes.

reply »

PCB Assembly Equipment Auctions

PCB X-Ray Inspection System