Caused by pressure from trapped gases during reflow. Shorting: Solder bridging on the perimeter pads.
The IPC-7093A standard!
Because BTC joints are invisible, IPC-7093A mandates (2D or 3D). The PDF includes example x-ray images showing acceptable vs. unacceptable void distributions. It also covers electrical testing limitations—since electrical tests often pass even with severe mechanical defects. ipc-7093a pdf
Post-reflow verification of BTCs requires specialized methodologies due to hidden solder joints. Inspection Methodologies
For the next three hours, the lab was silent except for the hum of the rework station. Using the IPC-7093A PDF as their guide, they didn't just adjust the temperature; they changed their entire methodology. Caused by pressure from trapped gases during reflow
Understanding IPC-7093A: The Standard for Bottom Termination Components (BTCs)
Adhering strictly to the standards defined in the IPC-7093A framework ensures that bottom termination components perform reliably over long lifecycles, mitigating field failures caused by thermal overheating, structural cracking, or electrical shorts. Because BTC joints are invisible, IPC-7093A mandates (2D
Elena leaned in, scrolling through the digital pages. "I see it. It details the via-in-pad processing. We’ve been plating the vias under the BGA, but this document suggests specific filling methods to prevent solder wicking away from the joint."
“All voiding is bad.” Truth: IPC-7093A acknowledges that 100% void-free soldering of large thermal pads is impossible. Small distributed voids (e.g., 5–10% total area) are harmless.
Reflowing BTCs demands strict control over the thermal profile to eliminate volatile chemicals before the solder liquefies.
The standard advises on specialized stencil apertures (e.g., cross-hatching or window-paning) for the central thermal pad, typically reducing the printed paste area to 50–80% of the total thermal pad area.