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top side remelt?

Views: 3278

Amy

#48635

top side remelt? | 26 March, 2007

Anyone knows about the top side remelting requirement for wave soldering process? Is there any standard & procedure to follow? What temp can cause the solder for top side to re-melt?

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#48638

top side remelt? | 26 March, 2007

Hi Amy,

183 degrees C if it's 63/37 paste.

For wave solder, your guide should be your flux. Follow your flux mfgers suggested pre-heat. Most mfgers go by top side temps.

Your wave solder pot temp is determined by your bar solder mfger.

The engineer puts it all together and runs product without any defects.

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#48639

top side remelt? | 26 March, 2007

The temperature that will melt solder holding top side SMT components during wave soldering depends on the alloy of that solder. So, for example, you'd expect: * Near eutectic SnPb solder to melt around 215*C. * LF to melt around 240*C.

It's common to see solder on top side components remelting near via, because via can act like heat pipes that conduct the heat of the wave solder pot to the top side of the board. If this is what you see, consider having the via pluged or caped. Covering the via with heat resistant tape works as a short term fix.

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#48641

top side remelt? | 26 March, 2007

Unless those vias are used for ICT or test.

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#48642

top side remelt? | 26 March, 2007

Someone had a fiiiine weekend.

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stepheniii

#48643

top side remelt? | 26 March, 2007

I don't do wave soldering but want to see if I understand the question here. Do you want previously soldered component joints melting when you wave a board? I don't think you really want that? Or is it you want to avoid it? Are you talking SMT parts? they would pretty much be the only ones to be there to remelt.

Or perchance are you talking about topside fillets on PTH parts?

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#48648

top side remelt? | 26 March, 2007

Not really. Spent half of it at work. And you? Did you have a fiiiiine weekend?

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Amy

#48655

top side remelt? | 26 March, 2007

Yes, I have tested some boards, and found that most QFPs which near the via will have the higher temperature. One of my customer requirement is to have the temp less than 200 deg C for top side. We were using the hi temp wire to solder the QFP's for profiling, and the peak temp was around 205 to 215 deg C. I am wondering if there is any standard for leadfree remelting procedure for both wave soldering and reflow. (remarks: I am using SAC paste for top side, and tried both SCN and SCS7 for wave soldering, but results are the same).

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#48661

top side remelt? | 27 March, 2007

There is no "standard" or "procedure". Your customer is putting a requirement on you because this has probably lead to weak QFP solder joints breaking in the field or non-functioning units due to co-planar QFP legs. I�ve been there done that. Had to speed our waves up about 1 ft per minute to eliminate this.

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#48663

top side remelt? | 27 March, 2007

Amy,

One way you can drastically lower the peak temperature of your QFP and prevent it from re-melting is to lower the solder pot temperature. If you're running 63/37 in your pot, the typical range for these is 460�F to around 500�F. You will need to look at your bar solder manufacturer's technical data sheet. Also, if you make this change, perform some experiments on your worst-case-scenario assembly, and watch out for top-side wetting. That's the variable most affected by a lower pot temp.

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