Recommendations for the removal of Humiseal UV cure conformal coatings

Source：Humiseal.com / Editor：Ellsworth Adhesives

UV curable conformal coating materials such as HumiSeal UV40 are frequently used in military, aerospace and automotive applications due to superior resistance to chemicals and mechanical stress. These properties make them difficult to remove when rework under the coating is required.

There are 3 methods for the removal of HumiSeal UV conformal coatings

1. Mechanical removal: Powder Micro Abrasion

2. Thermal removal: Burn Through

3. Chemical removal

All three methods will effectively remove the coating, depending on the process requirements, to allow individual component replacement and subsequent re-coating.

1. Mechanical Removal: Powder Abrasion Method:

There are several types of abrasive powders available for conformal coating removal including Carbo Blast, Plastic Blast and Soda Bicarbonate. Carbo Blast has been proven to be the least aggressive and successfully removes HumiSeal UV cure conformal coatings without affecting the solder resist or components. Made from wheat starch crystals it is the mildest of the available powders and does not cause any mechanical damage to the PCB. Carbo Blast is nontoxic and 100% water soluble.

For best results when removing HumiSeal UV cure conformal coating, blast the coating for short periods with a high air assist. A longer exposure with a lower air assist may lead to damage of the solder resist and components.

2. Thermal Removal: Burn Through Method

De-soldering techniques can be used to burn through or degrade a conformal coating. The temperature of the soldering iron decomposes the coating into a powdery solid that is easily removed from the substrate. This allows access to the underlying solder connections for component removal and replacement.

For best results when removing HumiSeal UV conformal coatings by thermal displacement, solder through the coating for a short period of time (<10sec.) with a high tip temperature. A good starting point is approximately 450C. If the coating does not burn in less than 10 seconds, then increase the tip temperature by 20C. If the coating thickness is greater than 300 microns a longer exposure will be needed which could potentially lead to damaging the solder joint and the solder resist underneath.

3. Chemical Removal Method

HumiSeal UV conformal coatings can be removed using select strippers after UV cure, before the secondary moisture mechanism has completed.

HumiSeal UV40, UV50LV and UV40-250 can only be removed using Stripper 1100 once the coating has been UV and moisture cured.

HumiSeal UV50, UV500 and UV500LV can be removed with the correct HumiSeal chemical stripper. Recommended strippers are HumiSeal 1080A, 1090 and 1100.

Ellsworth Adhesives is authorized distributor of  Humiseal® all over the world. Please feel free to contact us for immediate assistance with a technical request.

References:
https://blog.humiseal.com/improve-precision-and-reduce-time-when-removing-conformal-coatings
https://info.humiseal.com/hubfs/RECOMMENDATIONS%20FOR%20THE%20REMOVAL%20&%20REWORK%20OF%20HUMISEAL%20UV%20CURE%20CONFORMAL%20COATINGS%20White%20Paper.pdf