Ball grid array (BGA) is a type of surface-mount packaging used for integrated circuits. During pad design and stencil design of BGA-style component, you may encounter various issues. How to cope with these issues? This article will present solutions.
1. No treatment for via on the bottom of BGA. BGA pads comes with via, leading to solder ball runoff with solder during soldering; PCB fabrication without solder masking would cause solder and solder ball to run off through the via adjacent to the pad, leading to missing of solder ball;
2. Improper design of BGA pad solder mask. The through hole on the PCB pad would lead to runoff of solder, which could be avoided by adopting micro hole, blind hole or plug hole technique in high density assembly. BGA usually comes with via on bottom and the solder on the via would impact the reliability of BGA soldering after wave soldering, which could lead to short circuit of component.
3. BGA pad design. The exit routing of BGA pad does not exceed the diameter of pad by 50% and the exit routing of power pad is no shorter than 0.1mm, then the exit routing could be widened. To prevent deformation of pad, the solder mask opening is no larger than 0.05mm.
4. Pad size is not standard, too large or too small.
5. BGA pads are of varying sizes and the solder points are irregular figures of varying sizes;
6. BGA outlines is too close to the edge of component body. The whole component should be within the marked lines; the distance between outlines and edge of component package should be larger than the half (1/2) of component’s soldering end size.
To the above issues, VayoPro-DFM Expert software developed by Vayo Technology has provided solutions. DFM Expert comes with 1500+ design & assembly checking rules, and you could set corresponding BGA checking rules to perform detailed DFM analysis on the PCB design data. After the automatic analysis, the issues could be recorded in DFM analysis report for design personnel’s reference and to improve the BGA pad design quality.
1. The designed size of pad is usually smaller than solder ball by 10%~20%;
2. The stencil aperture is larger than BGA pad by 10%~20%;
3. BGA opening rule: aperture’s diameter 0.50-0.68mm for 1.27pitch; 0.45-0.55mmfor 1.0pitch; 0.35-0.50mm for 0.8pitch; 0.28-0.31mm for 0.5pitch.
To the issue of BGA pad stencil design, Vayo-Stencil Designer software developed by Vayo Technology has provided solutions. Stencil Designer software comes with a power stencil aperture library, which could learn into previous stencil aperture design and pattern. To solve the above issue, you could use the software to learn the aperture patterns corresponding to the BGA pads of different pitches in advance, later during stencil design of such BGA pads, the process could be completed automatically by calling the stencil aperture library.
Besides above two solutions, Vayo Technology also provide several other solutions to the PCB manufacturing & assembly issues, including 3D DFM/DFA analysis, DFX execution system, stencil know-how digitalization, DFT / testability & DFT strategy analysis, SMT specialized CAM tool, visual aids work instruction, board view & fast query, Gerber view & conversion, etc.
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