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Reference: viscosity, hardness

Potting Problems and their Solutions

Here are solutions to some potting problems.  The problem is listed and then the solution.   If you do not find your problem here email us and we will give you suggested solutions. 

Contents: not hardening, soft spots, cracking, SMT PC board fails, mottled surface, bubbles in/on top, hard at room temperature but liquid at elevated temperature, Cracking on cure, cracking on temperature cycling, lack of adhesion

1. The resin system will not harden .

Solutions:

a. Check mix ratio by weight. Volume ratio is not accurate enough

b. Premix resin and hardener before weighing ratio so filler is uniform. 

c.   Check the temperature of the potting compound and of the part to be at room temperature or the elevated temperature needed to harden the potting compound.

d.  See #2 soft spots.

e. Mixing completely.  If  MMD equipment is used try dispensing an amount and then mixing it by hand in a cup and compare to non-hand mixing.  If gel time is different change the static mixer to one with a step in it ( two different diameters).

f. Check resin and hardener to see if it has crystallized.  If it has then warm in an oven to melt the crystals

2. There are soft spots in the hardened potting compound.

Solutions:

a. Machine mixing: adjust machine so it does not phase. See MMD problems.

b. Hand mixing: after mixing the resin and hardener in a cup pour in to another clean cup, mix and then pour in to unit.

c. Check compatibility of wire insulation with the potting compound.

3. Cracking of the potting when temperature cycled.

Solutions:

a. Gel potting compound at a lower temperature.

b. Use a higher filler content (lower CTE) potting compound.

c.  Use a more flexible potting compound.

d.  Cocoon the unit with silicone and then pot it in the harder potting compound.

4. SMT PC board fails when temperature cycled.

Solutions:

a. Use a potting compound with a Tg below the lowest temperature that the unit is cycled.

b. Use a very highly filled, very low CTE potting compound and gel it at the lowest temperature possible followed by a post cure at normal cure temperature.

5. Surface of the potting is mottled in appearance.

Solutions:

a. Use a hardener that does not have amine blush.

b. Pour units in a low humidity area.

c. Change potting compound to a non-blush system.

6. Bubbles in/on top of hardened potting compound.

Solutions:

a. Machine MMD: reduce the pressure of the gas on resin and hardener.

b. Machine MMD: stop air leaks in lines.

c. Vacuum resin mixture after mixing.

d. If urethane potting compound and the bubbles are very small moisture is in the compound so back fill with Nitrogen not air.

7. Hard at room temperature but liquid at elevated temperature.

Solutions:

a.  Check mix ratio by weight. Volume ratio is not accurate enough.

b.  Premix resin and hardener before weighing ratio so filler is uniform.

c.  Check the temperature of the potting compound and of the part to be at room temperature or the elevated temperature needed to harden the resin system.

d.   See #2 soft spots.

e.  Mixing completely.  If  MMD equipment is used try dispensing an amount and then mixing it by hand in a cup and compare to non-hand mixing.  If gel time is different change the static mixer to one with a step in it (two different diameters).

f.  Check resin and hardener to see if it has crystallized.  If it has then warm in an oven to melt the crystals.

8.  Cracking on cure

Solutions:

a.  Reduce cure temperature

b.  Reduce mass of resin system

c.  Change potting compound to a slower curing material.

9.  Cracking on temperature cycling in operation of the unit.

Solutions:

a.  Gel at lower temperature.  See shrinkage.

b.  Remove sharp corners on unit

c.  Increase thickness of potting compound to at least 1/16 inch.

d.  Reinforce cracking areas with glass fiber or cloth.

e.  Change resin system.  See Potting Hints.

10. Lack of Adhesion to part

Solutions:

a.  Clean part of oil, mold release, flux and dirt.

b. Use primer or chemical treatment. See Primer suppliers

11. Foaming

Solutions:

    a. Moisture contamination of polyol - back fill tank with Nitrogen or use air drying cartridge for make up air with new material.

    b. solvent contamination if MMD machine was cleaned with solvent - purge machine with new materials.

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Last Modified: March 28, 2015