Anyone know the cause of crack in inductor on PCB?

Question

Picture is shown here. http://wasted.talents.googlepages.com/MVC-003F.JPG

Do provide me a possible root cause. I am thinking of pop-corn effect due to moisture within, but I do not think this inductor is MSL-3.

Would be great if you can provide me with other possible causes of components cracks in PCB.

Answer 1

I've had similar problems (what a headache!!).

Yes, the cracks do look like trapped moisture. Remember, cracks are always tensile in nature, so the cracks reveal the direction of the tensile stress (radially outward in your case).

Drying the parts is difficult: just heating them up in an oven will not dry the parts out - you must use a desicator oven to actively remove the moisture trapped in the plastic over a 48 hour period, or, put the parts in a high vacuum chamber for 48 hours to dry them out.

Just asking: did you look very carefully to see if the parts were cracked when you received them, or are you sure they cracked during reflow? If the cracks existed before you received the parts, then you will be able to see the cracks under a microscope (they will be small, but visible).

IF after you do a proper job drying the parts out (48 hours drying), and they still crack, you have a thermal expansion problem. Don't overlook this possibility. If the parts get hot and expand relative to the PCB, you can transfer stresses from the solder pad up to the coil adhesive. Also, PCB board flexing can cause this kind of mechanical stress problem.

You may find that your coil manufacturer doesn't care about your cracking problem - after all, you are only losing, what, 5% of your production? He only has a 5% investment in your coils - a pretty small amount. If this is the case, change manufacturers. If you can't change manufacturers, you may need to make a trip to Asia.

You can pre-bake the coils at a facility with the proper drying ovens, then package the dried parts in plastic bags with dry nitrogen and silica gel desicator bags. The parts will stay dry enough to be usable for a several months. Double bag if you need longer shelf life.

These problems are problems your contract PCB assembler should be helping to identify and help you solve. They encounter this stuff every day.

Answer 2

That is probably a good posibility of internal moisture, but the crack itself looks as if it were started in the center of ur inductor about 1/3 the way from the bottom right as shown in your picture. I whould look into the handling of the parts prior to finding the crack. Was the crack identified after your solder process?

But without seeing the board and knowing all of your processes...you have a lot of variables that you need to eliminate as possibilities.

Answer 3

Excessive current / heat + trapped moisture?
I think you are correct in your assessment, despite any msl category, if applicable, for the device - moisture trapped under the wrap and some heat could result in the example in the picture.

Answer 4

http://www.4fpcb.com/

Answer 5

Stay away from crack