Are There Noticeable Losses from PCB Solder Mask?

[@GremDR]

Also, a very convenient and fast way to open the solder mask over the track: 1) Select the desired copper tracks: 2) In the Properties tab, check the box in the section Solder Mask Expansion; 3) If necessary, you can set the width of opening in order to free the nearest area near the conductor from the mask.

[@petersage5157]

I noticed you didn't include, or even discuss, regular hot air solder leveling as an option for "plating" on exposed tracks. I take the HASL process is a lot less controlled, so the surface roughness would be unfeasibly unpredictable?

[@Zachariah-Peterson]

Unfortunately the graph that I show does not contain my dataset and I have not done research specifically into the roughness present in HASL surface treatments. So I cannot say for sure whether HASL will be better or worse.

[@emmatitova2154]

I had no idea solder mask affected this. I thought it was to make wires stable or a protective coating for physical damage.

[@Zachariah-Peterson]

Solder mask also performs this function. Just because there are some losses on the lines from solder mask does not mean you should remove solder mask from every design. In most designs you will not notice if the solder mask is removed or if it is kept because you will not notice the effects of the solder mask until operating in the multiple GHz range of frequencies.

[@stephenjbro]

Thanks for the video, this was incredibly enlightening. I had often made boards with removed solder mask and hadn't noticed a measurable difference between ENIG and ImAg (on RO4350B laminate). There were many factors at play and I am no longer working on RF boards, but this data you've shared is compelling. One question I do have though: why do MMIC manufacturers (for instance, MACOM) often opt for removing solder mask on thru microstrip lines on eval boards even when using an ENIG plating? Is this information on surface plating vs. copper roughness simply not commonly known?

[@trophosphere]

Soldermask will also change the characteristic impedance of the microstrip and since soldermask thickness is not that well controlled it tends to have a rather bigger unpredictable effect compared to the surface roughness of the plating. Lossess, as long as they are predictable, can be compensated for but unit to unit changes in characteristic impedance are a bit of a bigger headache.

[@cvillf4694]

Hi Zach, what about Hard Gold for HF? Could it be a good choice compared to ImAg?. Thank you

[@Zachariah-Peterson]

I do not have any insertion loss data on hard gold as a good alternative to silver. In terms of durability it is a better option than ImAg, and it has lower loss than ENEPIG without losing durability. But it is much more expensive than ImAg and ENIG/ENEPIG.

[@SodaKillz12]

Are the losses created because the solder mask dielectric material weakens the electric field to ground? Thanks!

[@Zachariah-Peterson]

If you're looking for the physics based answer, the reason is for absorption of electromagnetic radiation in the dielectric. The electromagnetic field around the trace is not static, it is a changing field that interacts with the dielectric. The dielectric becomes polarized and relaxes at a characteristic rate that depends on the atomic structure of the material. During polarization and relaxation, some of that energy is lost to the dielectric. In crystalline dielectrics, the lattice vibrations (phonons) can also interact with the electromagnetic wave. When the frequency of the wave matches the phonon frequencies, energy can be transferred from the wave to the lattice, which is another mechanism of absorption.

[@simonebiuso3098]

Hi