Solder thieving is the movement of liquid-phase solder metals away from their deposited location during the reflow process. Without a proper connection between the part and the printed circuit board, parts will have inadequate mechanical, thermal, and electrical connectivity to the circuit board. This problem primarily affects via-in-pad designs but can affect via-near-pads and unprotected-copper areas as well. Failures can be seen in parts ranging from complex Ball-Grid-Arrays (BGA) to small active and passive components.
The problem appears during the assembly process and is often blamed on the assembler. But in reality, it can be traced back to a single design decision during fabrication: whether or not to tent/fill/cap vias. Designers often think that filled/capped vias are a luxury they cannot afford. But that single bad decision can lead to a board having to be reworked at the assembly shop or completely refabricated. A board made with open vias in pads or vias near pads will cause assembly issues. The usual end result is that engineers have to pay twice as much to make the same panel — the “cheap” way produces an unusable product, and the board has to be reworked or remanufactured at twice the original expense.
The presence of holes in or near pads and the lack of solder-mask boundaries can allow the solder to flow or spread from the pad while in the liquid phase. If the via cavity fills with solder, there will be insufficient material present to allow intermetallic bonds to form between the solder, the pad, and the part. Fortunately, there are a variety of design options available to prevent solder thieving in your next design including:
- Via Tenting
- Non-conductive via filling
- Via Capping
- Conduction Via-Filling
For details on each of these solutions and how you can implement them in your next design, download this free whitepaper: