Soldering of NRF52840CKAA. General recomendations and requirements for soldering paste pattern

[Vladimir Aparin]

Hello,

we starting the production of first lot our devices on NRF52840CKAA (WLCSP).

We get some issues with manufacturing, which can be separated into to 2 parts:

1. General recomendations for reflow process.
   We found the nAN-40 for aQFN, where some details has provided, Can you provide us the same application note as nAN-40 but for WLCSP?
2. Pattern for soldering paste.
   This point hasn't described nowhere. Can we get recommendation here?
   We need to know:
   1. thickness and  size of apperture
   2. type of paste
      In nAN-40 we see Type 4 (25-45 um) as recomendation, but it should be Type 3 from  IPC J-STD-005. Please check it too.

Best regards.

[Andreas]

Hi,

 

1. See nAN-38 for recommendations on our WLCSP parts. UBM diameter for nRF52840-CKAA is 180µm.

2. Solder mask and stencil mask recommendation for aQFN is described in table 2:

There is a typo in the paste type as you say, Type 4 is correct, but it should be 20-38µm. We still recommend that you run this by your fab to get their input.

 

Best regards,

Andreas