Mail*Link¨ SMTP [TECHNET] BGA DFM and thermal management A PCB design engineer asked me: What potential difficulties will he see by placing numerous components under a BGA? My answers are: - Affect BGA solder joint reliability due to less compliance. - Can cause insufficient support at repair if too dense. - The bottom component can affect x-ray image quality (especially Metal Cap.) - In case that no solder mask is required to plug the vias in design, then difficult to apply masking tape before wave soldering if needed However, due to density restrictions, he has to do it. I think the above are desired but not mandatory, is it right? He also asked: does having four power planes affect the thermal transfer at all? Any answers? Thanks, Yuan