Coating WLCSP for Light Sensitivity

[FA]

Hi,

The nRF51WLCSP needs IR blocking coating and I found here that an example epoxy can be Epo-tek 320. I just want to check if there is any specific time for covering the pins, i.e., should it be done exactly after soldering the chip to the board OR it can be done (lets say) a couple of days after mounting?

Thanks!

[MartinBL]

Hi

There are no long term effects or permanent damage done to a WLCSP if you expose it to IR light. You can wait as long as you want before you cover the pins.

Silicon is translucent to IR light and the transistors in the SoC will basically start to act as phototransistors when exposed to light in this spectrum. This is especially noticeable in the analog parts of the SoC and IR light will cause the radio's carrier frequency to drift faster than normal. When you are transmitting data with an uncovered WLCSP the carrier frequency might eventually drift out of the admissible range and you will lose connection.