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I am evaluating a couple products -- lighting ballasts -- and noticed one of them seems to use G-10 as the PCB laminate. I assume that the beige, solder-mask-free top layer is the clue.

Top: Board1, top

Bottom: Board1, bottom

Given that FR-4 is Flame Retardant, whereas G-10 is not, I prefer to stay away from the latter laminate. But I cannot say for sure if the second board uses FR-4 or not.

Top: Board2, top

Bottom: Board2, bottom

It appears that the second board has more of the FR-4 look to it (that pale green), but that could just be a top-layer solder mask.

Am I on the right track here? Is it even possible to tell the difference between G-10 and FR-4 like this?

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  • \$\begingroup\$ Could the top one be phenolic-based? Bottom one does look more fibreglass-based - wouldn't care to guess further than that. \$\endgroup\$ – glen_geek Aug 30 '18 at 20:39
  • \$\begingroup\$ There are so many different types of PCB material out there you'll never identify it by looking at it. If you're worried about flammability, cut a piece off the edge and try to set it on fire. Do the potting compound too. \$\endgroup\$ – Jack B Aug 30 '18 at 20:55
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The top one looks like a cheap paper-based phenolic board eg. CEM-1/CEM-3. The outline and holes appear to be punched, which is very common for low end consumer products and power supplies. It punches fairly nicely under the right conditions, is cheaper and wears the tools less than epoxy-glass laminates.

Eg. Nan Ya Plastics CEM-1-97

The bottom one looks more like epoxy-glass such as FR4.

You can test for UL94V0 with a Bunsen burner following the procedure. Basically it's not supposed to keep burning (much) after the flame is removed.

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Am I on the right track here? Is it even possible to tell the difference between G-10 and FR-4 like this?

The color difference is in the solder mask. You won't be able to tell the difference between G10 and FR4 by look or feel, they are essentially the same from a materials perspective. Many manufacturers list datasheets with FR4 and G10 as the same product.

You could tell chemically if you could get an analysis done to check for bromine, as FR4 has a bromine additive to give it it's flame retardant capabilities, G10 does not.

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You could apply a flame to the corner and see if the flame self-extinguishes in 30 seconds under a fume hood.

There is a logo ® partially exposed in silkscreen for the ratings.

CEM-3 is very similar to FR4. Instead of woven glass fabric CEM-3 has a milky white color and is very smooth. It is very popular now in Japan.

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