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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Greg Curler

#15956

Waving TSOPs | 8 May, 1998

As usual, we are faced with too many components and not enough board on a new design. Does anyone have experience wavesoldering .025" pitch TSOPs on the bottom side? Any advice is appreciated. Greg

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Chrys

#15959

Re: Waving TSOPs | 8 May, 1998

| As usual, we are faced with too many components and not enough board on a new design. Does anyone have experience wavesoldering .025" pitch TSOPs on the bottom side? | Any advice is appreciated. | Greg Sounds scary, particularly from a reliability perspective. Can you cluster the bottomside SMT together and use a selective soldering fixture to shield them?

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Steve Gregory

#15960

Re: Waving TSOPs | 8 May, 1998

| | As usual, we are faced with too many components and not enough board on a new design. Does anyone have experience wavesoldering .025" pitch TSOPs on the bottom side? | | Any advice is appreciated. | | Greg Hi there Greg! First, I just gotta say to try and keep from waving them if you can...not saying it can't be done, but if you can keep from having to do that it be mo' betta... I've not waved TSOP's before, but I have waved 25-mil pitch 100-pin QFP's before. It was at last years NEPCON East down at the TAC line. Ray Rua came up with this board that we did there. It actually turned out okay, BUT there were some little "tricks" that made it happen. First, not just any 100-pin QFP works well. The shape of the leads and where the bends were makes a difference. The length of the shoulder of the lead (where it comes out of the package) can't be too long, the same goes for the foot too. If either are too long you'll get bridges. You need a good bit of room on the pads as well, in order for the solder to have a good area to start wetting to. There also were thieving pads placed on each of the QFP's corners...they almost looked like the shape of a pie-wedge. Another thing that was done, was to put the board into a fixture so that the QFP crossed the wave on a diagonal. How practical is this? I don't think it was very practical, I didn't look closely for popcorning or anything like that, it was only a demo board, but I imagine that's a real concern. Just try to keep it all on one side if ya' can!!! -Steve Gregory- | Sounds scary, particularly from a reliability perspective. Can you cluster the bottomside SMT together and use a selective soldering fixture to shield them?

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Bob Willis

#15957

Re: Waving TSOPs | 9 May, 1998

The first thing is all the TSOP suppliers like Intel do not rate the parts at normal temperature used in wave soldering. The spec is less than 230C so you have the reliability issue to consider and no one to blame when they do not work. You also have more of a cracking problem than with QFP. Wave soldering devices at 0.032" is fine, 0.025" can be done but 0.020" lots of shorts and I know as I have a customer doing it?

| As usual, we are faced with too many components and not enough board on a new design. Does anyone have experience wavesoldering .025" pitch TSOPs on the bottom side? | Any advice is appreciated. | Greg

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Greg

#15958

Re: Waving TSOPs | 11 May, 1998

Bob, The responses to my question kind of supported my first instinct to avoid waving TSOPs. Plan B may be to find a compliant pin connector and convection reflow both sides. Any comments? Greg : The first thing is all the TSOP suppliers like Intel do not rate the parts at normal temperature used in wave soldering. The spec is less than 230C so you have the reliability issue to consider and no one to blame when they do not work. You also have more of a cracking problem than with QFP. | Wave soldering devices at 0.032" is fine, 0.025" can be done but 0.020" lots of shorts and I know as I have a customer doing it? | | | As usual, we are faced with too many components and not enough board on a new design. Does anyone have experience wavesoldering .025" pitch TSOPs on the bottom side? | | Any advice is appreciated. | | Greg

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