We have a problem with one of your isolators ADuM1447 where from the datasheets package drawing the cheepage distance for the part is 5.6mm (enaugh for our purpose) but in the VDE report its stated 5.3mm (does not comply to standard in our case). Where is the error in your datasheet or in VDE report?
I always defer to the agencies measurements. 5.6mm on the drawing is the maximum body width under the JEDEC package standard. The drawing also says it could be as small as 5.0mm.
Unfortumately due to the way that JEDEC spedcifies their packages. The creepage can not be reliabley determined from the drawing. JEDEC tends to dump all of the packge tollerances onto the path that is required for creepage. For example, there is no spec for the distance from the end pin to the end of the package . In addition, there is a floating metal tie bar, that is required as part of the package manufacturing process, that must be subtracted from the creepage since it is right in the path. Not problems for most products, but in isolation, it directly impacts the creepage. So the agencies actually measure the package. CSA measures 5.1mm, VDE measures 5.3. Table 13 in the data sheet calls out 5.1 so we cover the worst case.
For your issue, have you taken into account that our Mold compound is material group II. That usually reduces the required creepage by about 33%.
Yes the creepage was determined via the datasheets package drawing using the least favorable distances and we came to 5.6mm, also when measuring the package itself. As the package has thickness also. But we did not think of the floating metal tie bar. The 5.1mm specification in datsheet was overseen. We have taken the material group II into account. As no other product is so low power as the ADuM1447 conformal coating is the only solution to the problem to Achieve pollution degree 1 and so smaller creepage distances. Does Analog devices recommend a coating or did you tested some? In The datasheet there is mentioned the device is rated up to max working voltage of 849V reinforced insulation per VDE, this is probably with conformal coating applied?
We do not have any recommendations on conformal coating or potting. We simply do not have a great deal of experience on system level manufacturing.
VDE offers a component level standard, where the working voltage, transient withstand, Reinforced insulation, creepage and clearance are evaluated somewhat independently. Your system level standard is what ties together the working voltage to the creepage and clearance. Just because VDE says we can tolerate a working voltage does not mean the package has the creepage to utilize it. This is to allow flexibility in using different system level standards where the requirements can vary somewhat, eve though in recent years harmonization has reduced the usefulness of this approach, some standards like IEC61010 are still a bit off of the norm.