Tears or Cracks in Lead-Free solder joints

Lead is for bullets, not for soldering.

Sulfur is expensive to remove from lead.

http://en.wikipedia.org/wiki/Planned_obsolescence

Send me a photo,

I suspect the following:

Lead free solder: Sn/Ag/cu system? or Sn/Ag system.

The silver in essence is a flux agent in this system lowering the mp of the system. However, during melt and reflow the silver precipitates into almost a pure silver phase in the solder. This will crack the solder joint if the solder process was too long giving time for the silver rich phase to migrate to the surface.

Hi Ydobon,

To answer your question,we are using a standard SAC305 alloy supplied by Cookson Electronics. It says "Alpha Lead-Free Wave Solder Bar" on the outside of the box.

Also bear in mind that we have just done some trials this weekend gone by and we tried varying everything in the process. Standard pot temp of 255C, Hot pot at 275C, cooler pot at 245C, Standard conveyor speed of 110cm/Min,faster conveyor speeds of 220cm/min and slower conveyor speeds of 80cm/min - nothing got rid of the cracks or tears :(

How is your atmosphere and temperature ramp down? Just a thought......

The atmosphere is in air. We are not using Nitrogen on our wave solder machine. Also we are not using any chillers or forced air cooling immediately after the wave. Our equipment is an Ersa EWS330 wave soldering machine. It does have a bank of fans after the boards exit the machine but my understanding is that these fans just cool the board down so that a person can handle it easier. Because there is an approx 30 second delay from the moment any point exits the wave to the time when these fans blow air on that point. Surely the solder has solidified long before this. And yes, we did try a run with the fans disconnected and it made no difference.

Found comments relating to lifting pads (especially on through hole) soldering relating the problem to non-eutechtic materials with pasty transition from liquid to solid creating stress from contraction during cooling and creating cracks.

Comment was that it is more common in the solders containing Bi.

(Source of info is a powerpoint presentation that was left at our site on CD by Multicore solder suppliers in 2003)

Thanks to everyone who replied to this thread.

After extensive investigation we actually discovered that this is an acceptable phenomenon in Lead-Free soldering.

The phenomenon is called a "Hot Tear" and seems to be accepted even by the IPC standards group.