
PCB Layout Recommendations
Lattice Semiconductor
for BGA Packages
18-17
PCB cross-sectioning is another method used to verify BGA and PCB quality and reliability. After a new process
has been developed or changed or when qualifying a new vendor, it is a good practice to get physical information
from the vendor on their BGA reflow. When trace/space and drill or laser tolerances are nearing their limits, board
yield can be as be as low as 50% for the bare board fab. Cross-sections give you a good idea if the process is cor-
rect but do not guarantee each batch or each board design will behave the same way due to layout dimensions,
thermal issues, flux/paste and alignment, etc.
Figure 18-17 shows a BGA cross-section that uses a non-soldermask over bare copper-defined pad. (NSMD) pad.
Figure 18-17. BGA Cross-Section
Figure 18-18 shows “offset” micro via stack routing between layers.
Figure 18-18. Cross-Section of Micro Vias
High-resolution video cameras are used for edge inspection to verify ball seating, distortion, solder wetting, flow,
contaminates, etc.
Figure 18-19 is a video view of a side/edge shot looking at BGA balls soldered down to the isp-