Abnormal inspection when checking by X-Ray machine

[Do Van Hiep]

Hello Experts,

When I use a X-Ray machine to check appearance of NRF52840 . But I found out that there were some abnormal phenomen as same as a photo below:

Any body can explain what they are and is it normal or defect?

Thank you.

[ketiljo]

You seen have too little solder paste applied. The center pad has some air bobbles but that's probably ok. The pads however are more concerning, some om them are circled here: 

Try to use a thicker stencil to apply more paste. 

[Do Van Hiep]

Hi Mr Ketiljito. Thank you for your recommendation. It's helpful for us.