Type XY conformal coating refers to parylene conformal coating.  Parylene gets the type XY from its’ full name, para-xylylene.   It was shortened to parylene and eventually type XY so that it could be grouped with the other conformal coatings (type AR, UR, etc.).

Type XY conformal coating application

Type XY conformal coating is applied through a vapor deposition process onto the material that is being coated.  This material is placed into a coating chamber.  Depending on the coating type and required thickness, typical parylene deposition rates are about .2/mils per hour, so machine runs can vary from as little as 1 hour to over 24 hours.  The process begins with raw dimer in solid state (these are:  Parylene C, Parylene N, Parylene D, Parylene AF-4, or other variants) being placed into a loading boat, which is then inserted into the vaporizer.  The raw dimer is heated between 100-150º C.  At this time, the vapor is pulled, under vacuum into the furnace and heated to very high temperatures which allows for sublimation and the splitting of the molecule into a monomer.   The monomer gas continues to be drawn by vacuum one molecule at a time onto the desired substrate at ambient temperatures in the coating chamber.  The final stage of the parylene deposition process is the cold trap.  The cold trap is cooled to between -90º and -120º C and is responsible for removing all residual parylene materials pulled through the coating chamber.

Type XY conformal coating thickness

One of the different factors to take into account when trying to determine the proper type XY thickness is the amount of clearance needed.  If it is a printed circuit board that is an enclosure, there usually will not be too many clearance issues.  However, in some cases, even an extra mil of coating can cause extra mechanical abrasion to the parylene which can result in a damaged type XY conformal coating film.

Another factor to consider is the dielectric strength required.  For applications that require higher dielectric strength, a thicker coat of parylene has higher dielectric properties than a thinner coat.  Trying to balance the dielectric strength issue with the clearance issue is a tight rope to walk and will usually require some testing to determine the proper balance.

To learn more about type XY conformal coating, download our free Parylene 101 guide: https://blog.paryleneconformalcoating.com//parylene-101-guide/