Common design issues for BGA pads include the following:
1. The vias at the bottom of the BGA are not processed. There are vias on the BGA pads, and the solder balls are lost with the solder during the soldering process; the PCB manufacturing does not implement the solder mask process, resulting in the loss of solder and solder balls through the vias adjacent to the pads, resulting in missing solder balls.
2. Poor design of BGA solder mask. Via holes on the PCB pads will lead to the loss of solder; in high-density assembly, micro-hole, blind-hole or plug-hole processes must be adopted to avoid solder loss; there are vias at the bottom of the BGA, and after wave soldering, the solder on the vias Affect the reliability of BGA soldering and cause defects such as short circuit of components.
3. BGA pad design. The lead wire of the BGA pad should not exceed 50% of the diameter of the pad, and the lead wire of the power pad should not be less than 0.1mm before it can be thickened. In order to prevent the deformation of the pad, the solder mask opening is not more than 0.05mm.
4. The size of the pad is not standardized, too large or too small.
5. The BGA pads are of different sizes, and the solder joints are irregular patterns of different sizes.
6. The distance between the BGA frame line and the edge of the component body is too small. All parts of the components should be located within the scope of the marking line, and the distance between the frame line and the edge of the component package body should be greater than 1/2 of the size of the component soldering end.
solution:
As shown in the figure below, the VayoPro-DFM Expert software independently developed by Wangyou Company has its own corresponding BGA inspection rules to conduct detailed DFM inspection of PCB data, record the problems found, and form a DFM analysis report for the designer's reference. , check for leaks and fill in the gaps, and solve the corresponding problems caused by the BGA pad design.
BGA pad design and stencil opening rules:
1. The design of the pad is generally 10%-20% smaller than the diameter of the ball;
2. The opening of smt steel mesh is 10%-20% larger than that of the pad;
3. BGA opening rules: 1.27pitch opening diameter 0.50-0.68mm; 1.0pitch opening diameter 0.45-0.55mm; 0.8pitch opening diameter 0.35-0.50mm; 0.5pitch opening diameter 0.28-0.31mm.
solution:
As shown in the figure below, the Vayo-Stencil Designer software independently developed by Wangyou Company can learn the corresponding opening model in the stencil library in advance when designing the stencil opening. We can map the BGA pads of different pitches to corresponding The opening model of the stencil is learned, and intelligent matching can be used when designing the opening of the steel mesh, or the model can be used manually to design the opening of the steel mesh.
