What 300 C means for a rack, in Fahrenheit

High temperature racks are rated in Celsius and a good many US floors work in Fahrenheit. The conversion is the easy part. What the rating covers is the part worth reading carefully.

The two numbers

200 C is 392 F. 300 C is 572 F.

For anything in between, multiply by 1.8 and add 32. A 150 C rating is 302 F. A 250 C rating is 482 F.

What a temperature rating actually promises

It is a statement about the rack keeping its shape and its properties at that temperature. It is not a statement that the rack is unaffected by heat, and it is not a statement about how long it can be held there.

Two things degrade in a rack that is worked hot. The first is dimensional stability, which is the one people expect: a rack that softens will let its slot pitch drift, and a drifting pitch is how boards start touching. The second is the ESD property, which is the one that gets missed, because a rack can come out of an oven looking perfectly straight while its surface resistance has moved.

A rating covers both. That is why a standard rack used slightly above its rating is not a small compromise. It can look fine and no longer do the job it was bought for.

When you need one

The obvious case is a rack that goes into an oven. Baking to remove absorbed moisture from moisture sensitive devices is the common one, and the temperatures involved are set by the device rather than by preference. Our note on baking MSD boards per J-STD-033 covers the conditions.

The less obvious case is a rack that never enters an oven but sits close to something that is hot. Reflow exit, wave, curing, a rack parked next to a chamber door. Nobody thinks of that as a high temperature application, and the rack sitting there is quietly being cycled.

Cycling is harder than a single peak

A rack that goes to temperature once and cools is under less stress than one that does it repeatedly. Repeated expansion and contraction is what loosens fixings and moves geometry over time.

If a rack is going through a thermal cycle as part of a routine process rather than occasionally, the rating you want has margin in it, not a rating that exactly matches your peak.

The practical rule

If the rack will see an oven at all, specify for the oven. If it will sit near heat rather than in it, find out what that position actually reaches before assuming a standard rack is fine, because ambient near a hot process is not room temperature.

If it will cycle repeatedly, leave margin above your peak rather than matching it.

Our high temperature racks list their rating on the product page in both scales. If you are unsure which side of the line your process sits on, send us the temperature and the dwell time and we will tell you plainly whether a standard rack covers it.