I plan to use the MPX4250AP as a boost sensor but was wondering where I can mount it? I am asking as i don't believe it is waterproof (this will be mounted on a hilux that will get wet). Preferably I mount it in the engine bay as close to the other OEM boost sensor as possible so I do not have to route a long hose to it from the cabin. This way i can ensure i won't have a lot of pressure drops. Can I mount it inside an enclosed box?
As mentioned on the support case submitted, protecting pressure sensors with a silicon grease is definitely the best way to use our products in harsh media. Unfortunately, we don't have so much experience in how to implement this solution 'industrially'. The grease fill is done under vacuum to avoid air bubbles. Usually, an offset calibration is necessary because the grease brings some mechanical stress that may shift the offset value. This solution was tested and seems conclusive.
Following to your inquiry, we would recommend using Parker O-lube silicone grease or DMS-T46 or T51. 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 is 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.
As said, you can use any silicon oil or preferably grease from other suppliers with high viscosity and high molecular weight.
Please review the following application note that would be worth to be considered in addition to the provided information.
AN3728: Media Compatibility for IPS PRT Pressure Sensors
I hope this helps.