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Lifting Pads and Tip Temperature
Lifting Pads and Tip Temperature
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Old 5th June 2010, 11:44 PM   #1
DreadPirate is offline DreadPirate  United States
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Default Lifting Pads and Tip Temperature

I'm using a good weller station wesd51 type I think. I have the iron set at my soldering temperature of 370 C or so. Kester recommends 320-380 C for the 63/37 I usually use. Anyway, by default I have been using this same temperature to de-solder and I'm wondering if it is too hot, as I'm lifting pads more than usual. I also notice on a recent project, that I did not lift the pads at all when de-soldering larger transistors, while the little small signal ones seemed to lift out quite easily. This leads me to believe that it is the larger transistors acting as heat sinks lowering the temperature and preventing pad liftings. So, have others come to the same conclusion that perhaps it is better to de-solder at a somewhat lower temperature than typical soldering?
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Old 6th June 2010, 07:48 AM   #2
Nisbeth is offline Nisbeth  Denmark
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Lifting Pads and Tip Temperature
What size tip are you using? It isn't the temperature in it self but the amount of energy transferred to the PCB that's the problem. The Weller temp. code is the temperature of the heating element and that temperature is going to drop more or less when it comes into contact with the component/PCB depending on the size of the tip.

/U.
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Old 6th June 2010, 11:05 AM   #3
DreadPirate is offline DreadPirate  United States
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So you have had more success preventing lifted pads with a finer tip?
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Old 6th June 2010, 11:30 AM   #4
wakibaki is offline wakibaki  United Kingdom
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This is a bit of a moot point as there is bound to be some variation in pad adhesion between PCBs even from the same manufacturer.

In my experience surface mount components and a hot-air rework technique offer the best success rate. Socketing thru-hole components can prove cost-effective, but getting it right first time both in terms of construction and design is the cheapest option. Any board that fails repeatedly in the same mode should be redesigned.

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Old 7th June 2010, 07:54 PM   #5
Enzo is offline Enzo  United States
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And using too low a temperature or too small a wattage iron can make more pads lift. An iron set to transfer enough heat to melt the solder quickly is what you want. Keeping heat on the pad too long is a good way to lift it. Solder and desolder with confidence. Timid application of the iron keeps the joint hot longer.

And sometimes wetting the joint - adding a little fresh solder - before desoldering make getting good thermal contact easier
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Old 11th June 2010, 01:16 AM   #6
adx is offline adx  New Zealand
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Yes, what they said.

I have found 370C (700F) is just under the threshold of pads letting go easily. 800F is too hot, they will come off in an instant. 600F is too cold, it takes too long which often results in ripping the pad off/out of the board from the combination of cooking the adhesive, solder freezing, and frustration. Of course it's a sliding scale to a point, but FR4 boards are usually very well standardised and often behave almost identically, some of the hobbyist board manufacturers' boards come apart a bit easier.

This was from helping set up soldering operations in a manufacturing environment (apart from the hobbyist bit).
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Old 11th June 2010, 02:52 AM   #7
kevinahcc20 is offline kevinahcc20  United States
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I have had very good results with the Ratshack solder sucker soldering iron - it's rated 40W (non adjustable) and there is lots of thermal mass in the tip assembly. The hole in the tip is lowered over the stub of the lead in the joint & it melts very quickly & vacuums up the solder quite effectively. I think it only cost $40 or so.
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Old 12th June 2010, 09:32 PM   #8
DreadPirate is offline DreadPirate  United States
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I'm definitely suspecting my 380 C typical soldering temp is on the high side, I'm going to set it back to about 350 C from now on and see how that works out.

The spring loaded desolder tool, which I just began using, seems much more effective than the bulb.


The desolder iron from RS is something like 12! Certainly worth a try at that price.
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