MCXA155 feasibility

[Vasilis_Skr]

Dear NXP community,

First of all hello. My name is Vasilis and we are currently designing in my company a power PCB that also needs to have a safety μCU that is going to measure some safety-critical signals. For that we have selected the MCXA155 family.

However, since the PCB needs to also deliver power, we want to use 2oz copper in the outer layers. Since the minimum clearances on 2 oz copper PCB's are higher than the regular 1oz, which of the offered packages is the safest to use in our application?

If it is not possible at all, we might have the option to scale back to 1oz, but we would like to avoid it, if possible.

Thank you in advance and I am looking forward to hearing from you!

Best Regards,

Vasilis

[luis_maravilla · Accepted solution]

Dear Vasilis

Could you please confirm how many layers are used in your PCB design?

According to the EMC Guidelines for MCXA14x/15x MCU Designs Chapter 3.1.1 PCB Stack-up design

The MCXA14x/15x MCU has a large number of signal interfaces. Therefore, it is recommended to use either a 2-layer or 4-layer PCB design.

The recommendations on the outer layers design for 2 and 4 layers are described in Chapter 3.1.1.1 - 3.1.1.2

The information in MCXA14x/15x Hardware Design Guide could be relevant to you as this document provides guidelines and recommendations for creating hardware designs based on the NXP MCXA14x/15x MCU.

The package used in the FRDM-MCXA156 [A154/5/6 MCUs]  is a LQFP100, that could be a reference to use the LQFP package in your design.

To consult the variety of package options and characteristics please refer to MCXA14x/15x Hardware Design Guide Chapter 2.2

Best Regards, Luis

[Vasilis_Skr]

Hey Luis,

First of all thank you for pointing me to the proper documentation!

Regarding your question, we are going to use 2 layers for our PCB, since the signals that the processor needs to monitor are quite few but very critical. 4 Layers is still an option if really needed.

In the specified stack-up, I see that 0.5oz copper + plating  (so around 1oz) is used. Nothing is mentioned for thicker copper layers, but I have checked with PCB suppliers and the minimum clearance for a 2oz copper PCB is around 0.15mm, which seems sufficient.

The LQFP100 or the QFN48 are the packages we are considering for the application, since they are most forgiving in terms of clearance between pads, with QFN having 0.25mm being the most likely candidate.

I will check the documentation thoroughly and proceed with designing. 

Thank you very much!

Best Regards, Vasilis