BGA General Info
Ball Matrix: (see examples on right)
Full Grid
Perimeter Rows
With Center Thermo Via
Staggered Array

Substrate Material:
BT (Bismaleimide Triazine) -- PBGA and SBGA.
Polyimide -- µBGA, flexBGA and TBGA
Ceramic -- CBGA, CLGA (Land Grid Array) and CCGA (Column Grid Array)

Ball Material:
Eutectic - Sn63/Pb37 - PBGA, CSP, flexBGA
Near Eutectic - Sn62/Pb36/Ag2 - LBGA
High Temperature - Sn10/Pb90 - CBGA
Lead Free - Sn96.5/Ag3.0/Cu0.5 - Sn95.5/Ag4.0/Cu0.5 - Sn96.5/Ag3.5

Ball Pitch:
Fine Pitch and CSP: 0.5mm, 0.75mm and 0.8mm
PBGA types 1.0mm, 1.27mm and 1.5mm

Thermal Pads:
Center balls to dissipate heat.

"Pop Corn" Phenomena:
Prior to assembly, it is recommended to bake BGA at 125°C for 24 hours to remove moisture and prevent delamination and cracking.

Thermal Mismatch:
Thermal mismatch occurs when mounting large ceramic CBGA (>31mm) onto laminate substrates, such as FR-4. Conversely, thermal mismatch occurs when mounting large Plastic PBGA (>31mm) onto ceramic substrates. During repeated temperature cycling, the solder balls on non-compatibly matched large PBGA and CBGA will tear away from the substrates.

Why BT is Used:
BT (Bismaleimide Triazine) is the popular material of choice for PBGA because its TCE (Temperature Coefficient Expansion) is mid-range between the TCE of FR-4 PC boards, copper and the silicon die which is attached inside the PBGA with adhesive.

Daisy Chain (See example right):
Used on dummy BGAs to perform continuity testing after mounting to the substrate (PC Board).

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