Hello Michael,
We don't have so much experience in how to implement this solution 'industrially'. Some customers have done this by placing a silicone grease fill over the pressure sensor’s port surface to protect the die and gel coat. A physical barrier can also be placed between the sensor and the media as to isolate the sensor. The grease fill is done under vacuum to avoid air bubbles.
We typically recommend to use Parker O-lube silicone grease or DMS-T46 or T51 http://www.gelest.com/wp-content/uploads/product_msds/DMS-T46-msds.pdf This type of grease is used by most of our customer without problems. In fact, the basic recommendation is to use a silicone oil (or preferably grease) with high viscosity and high molecular weight. In this case, the size of the molecules are big enough to limit the penetration of the grease inside our protective silicone gel which is over the die. In terms of contaminants, the silicon grease must be free of halogenures (Cl content < 50 ppm) to reduce the risk of bond pad corrosion. On the other hand, don't forget that whatever the material you will use, as soon as you put something on our gel you have a high probability to see some offset drift. This is coming from additional mechanical stress and/or gel swelling. The amount of gel and global mechanical design are usually also part of the offset drift. The AN1636 "Implementing Auto zero for Integrated Pressure Sensors" will help to correct the offset drift.
Best Regards,
Paulina
