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46 SMT007 MAGAZINE I NOVEMBER 2026 Solder Paste Volume When solder paste is used, the objective is to deposit a controlled and repeatable volume, not simply to add more solder. Too much paste can increase the risk of solder balls, bridging, or incon- sistent collapse, while too little can contribute to insufficient joints. The PCB site should first be prepared so the pads are reasonably flat and free of excessive residual solder. For standard BGA rework, the stencil aperture diam- eter will generally be based on the PCB pad size, leaving stencil thickness as the main variable used to control paste volume. A simple rule of thumb is that stencil thickness should be about one-third of the aper- ture diameter. For example, if the aperture is 12 mils in diameter, a stencil around 4 mils thick is a reasonable starting point. As the aperture diameter gets smaller, the stencil generally needs to become thinner so the paste can release cleanly and consistently. In practical terms, finer-pitch BGAs with smaller pads usually require thinner stencils, while larger- pitch devices can tolerate thicker stencils. The goal is to provide enough solder volume without making the stencil so thick that paste release becomes inconsistent or the bridging risk increases. BGA Rework Stencils Three common approaches are miniature metal, removable adhesive-backed, and stay-in-place stencils. Each can produce good results, but they behave differently on a real assembly. The choice usually comes down to access, quantity, pitch, and how much alignment assistance is needed. Mini Metal Stencils Miniature metal stencils are common and work well when sufficient access is available around the rework location. Their main advantage is dura- bility: They can be cleaned and reused for repeated rework of the same device. In practice, however, they require good physical access to the site and consistent contact with the PCB surface. Nearby components can make posi- tioning and printing more difficult on densely popu- lated assemblies. The stencil also needs to sit flat against the board; any distortion, bowing, or uneven contact can affect paste deposition and produce inconsistent volume across the array. Metal sten- cils work well when there is adequate room and support, but they are not always the most conve- nient option for tight rework locations. Removable Stencils Removable adhesive-backed stencils are the option we use most commonly for standard BGA rework. Because the stencil adheres directly to the PCB surface, it maintains good contact with the board and helps promote consistent solder paste deposi- tion across the array. After printing, the stencil can be peeled away cleanly without leaving adhesive K N O C K I N G D OW N T H E B O N E P I L E Figure 2: Miniature metal BGA rework stencil used for manual solder paste printing.