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Solder Paste Flux corrosive?

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GEB

#59853

Solder Paste Flux corrosive? | 15 September, 2009

Hi,

We're using solder paste opposed to solder wire for hand soldering certain components. We are also using high temperature soldering irons with 450deg C tips as we are soldering onto aluminium (IMS) PCBs. The quantity of tips which we go through seems to have increased from using solder wire to solder paste. Do you know whether the flux could corrode the tips? We're using a no-clean ROL0 flux 11.5% content and the datasheet also says it is low halide/ halide free.

If you need any more information please let me know. Any help appreciated. Thanks.

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#59859

Solder Paste Flux corrosive? | 15 September, 2009

What flux did you use when you soldered with the wire solder?

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GEB

#59862

Solder Paste Flux corrosive? | 16 September, 2009

The solder wire uses a ORL0 flux. The wire contains less flux at around 2.0-4.0%.

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CL

#59864

Solder Paste Flux corrosive? | 16 September, 2009

Are you using a SAC305 or high tin alloy? That will corrode the solder tip as well.

Chris

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GEB

#59866

Solder Paste Flux corrosive? | 16 September, 2009

Its SAC305 paste. Will that corrode the tip or the tin alloy?

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CL

#59867

Solder Paste Flux corrosive? | 16 September, 2009

That will definately cause a shorter tip life. The high tin in the alloy along with the higher temps are probably your culprit.

We have noticed a degredation it tip life when we changed from leaded to RoHS on standard PCB's.

Good Luck

Chris

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GEB

#59935

Solder Paste Flux corrosive? | 22 September, 2009

Hi Chris,

We've had another supplier say that it is the silver or combination of tin with silver that causes the corrosion. Would you agree?

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#59941

Solder Paste Flux corrosive? | 22 September, 2009

They could be correct about the silver if it weren't such a small portion of the connection. Study "electrochemical series of metals" to understand how metals react with each other.

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CL

#59983

Solder Paste Flux corrosive? | 25 September, 2009

Some information on the web regarding RoHS and tip life...

What problems are there for using Lead-free solder?

? Higher melting point of Lead-free solder may cause physical and thermal damage to components and PCB. ? Lead-free solder has poor wetting ability and therefore needs a more active (corrosive) ? Flux to improve wetting. ? Lead-free solder joints need longer time to solidify. ? The solder point will appear dull in color. ? The high tin content of Lead-free solder will shorten life time of the soldering tips.

How to cope with the above problems?

? Do not try to increase the temperature of the soldering tip to accommodate for higher melting point, because this will cause more damage to components and PCB. ? Also, higher temperature will only make soldering of Lead-free solder even more difficult because more oxidation will form causing even worse wetting. ? Keep using the same temperature as normal with tin/lead solder. ? Instead, choose the largest soldering tip possible for the joint, and use a high power soldering iron. ? This way, the larger tip (with larger volume mass) has better heat retention and the fast thermal recovery of the tip will help smooth out the Lead-free soldering process.

Why does Lead-free solder shorten life time of soldering tips?

? Tin itself is a very active metal. ? Tin reacts with the iron (Fe) layer of soldering tips and the iron layer is eroded away. ? The higher the temperature, the faster the erosion speed. ? With almost all Lead-free solder, the percentage of tin is over 90%. ? Since there is higher tin content, with higher temperature and presence of more active flux, the erosion of soldering tips occurs faster than regular tin/lead solder.

How should we care for the soldering tip to extend the life?

? Keep the tip the cleanest possible during use. ? Always TIN the tip before putting the soldering iron back in the holder. ? If you are not using the soldering iron for a while, e.g. over 10 minutes, turn off the soldering iron. ? Use the lowest possible soldering temperature.

Hope this helps.

Chris

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