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Double Sided Reflow - Low Melting Point Solders

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#40804

Double Sided Reflow - Low Melting Point Solders | 3 April, 2006

I have a less than perfectly designed pcb requiring double sided lead free reflow. Several components from either side will detatch using the standard process. If I was using Sn63Pb37 I would just dispense some adhesive after paste and cure at the reflow profile. No problem. Question 1. If we are using a SAC alloy are there any adhesives that will cure OK using a SAC style profile and survive for the second pass? Question 2. If this is not feasible, is anyone using a lower melting point alloy, (say 200 to 210 peak or less)for the top side second pass? I'm hoping/praying/trying to ensure there will be no Pb in terminations etc. Question 3. Anyone using fixtures on the bottom side second pass to lower the bottom side temp? Costly amd fiddly I would imagine? Question 4. For a SAC style profile is anyone getting delta T of around 40c between top and bottom with a Heller 1500 or 1700 with no bottom cooling? I can't. Question 5. Larry, can you ask the guy in stores for me?

Point 1. I have searched the fine SMTNET archives - it all seems to relate to pre Pb-free temps. Point 2. Heller 1500 or 1700 with no bottom cooling. (See Q4). Point 3. Yes I know, but I'm getting lazy, old, cranky, ugly and the Missus is going through the change. Besides the fish are on the bite and the beers are cold - icy cold! Point 4. He may be smarter than me. Any thoughts appreciated.

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#40814

Double Sided Reflow - Low Melting Point Solders | 3 April, 2006

How big are the parts? I've only seen a few parts that ever fell off. Double sided reflow is probably the most common these days

The surface tension is powerful.

I think the lower limit of temperature is what you would have to worry about with epoxy, and since you are raising the temperature not lowering, I really don't think you have to worry. If you made the temp hot enough to be bad for the epoxy then I believe your boards would delaminate anyways.

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RDR

#40815

Double Sided Reflow - Low Melting Point Solders | 3 April, 2006

Don't worry about the temp, and go fishin! seriously

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RDR

#40816

Double Sided Reflow - Low Melting Point Solders | 3 April, 2006

Don't worry about the temp, and go fishin! seriously

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#40822

Double Sided Reflow - Low Melting Point Solders | 3 April, 2006

Boy, you can say that again!

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#40849

Double Sided Reflow - Low Melting Point Solders | 5 April, 2006

Awww, come on guys, I should never have mentioned beer and fish. Lucky I didn't mention Elle.

OK, forget the points and questions 1, (probably correct there Stephen) and 5. Any comments on questions 2, 3 and 4?

This bloke's been stranded on an Island for 2 years. In the distance he sees a raft and swims out to it and drags it back to shore. Elle McPherson is lying supine on the raft dressed in a clinging wetsuit. She is not breathing. The bloke immediately starts mouth to mouth and after several tense minutes, Elle splutters and comes to life. "Oh my God, where am I?" she asks. "You have washed up here on this deserted island" replies the fella, "Iv'e been here for two years!". "That's terrible! How have you survived?". "Well, I catch the occasional fish and eat a lot of coconuts, dig a few yams and whatever else I can get" he replies. " Well", she says, "I have some supplies on me; would you like a cigarette?". "Oh", he says, "that would be unreal, I only had one packet when I landed here and they only lasted a day". She undoes a sealed pocket in the wetsuitand hands him a dry packet and a lighter. He lights up the smoke and takes a deep drag. The only thing he can say as he exhales is "Heavenly, absolutely heavenly". "How about a beer?" she asks, "there's two left that have been kept cold in the water". She undoes the side pocket in the wetsuit and hands over a beer. "Cheers", he says as he cracks open the cold tinnie that she passes to him. He can't believe his luck. A smoke and a beer after all this time! While he is considering his good fortune, Elle says to him, "You know, if you hadn't have saved me, I'd be dead by now. I really owe you my life and I want to repay you". With this she turns to face him and seductively starts to undo the main zipper of the wetsuit, whispering, "would you like to play around?". "COME OFF IT!", he says, "don't tell me you've got a set of GOLF CLUBS in there!".

Now can I get some serious answers?

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