1. Offset analysis of PCB daughter board
Before the PCB daughter board is fully assembled, there are two stacking methods. One method involves securing the daughter board to the edge of the motherboard using rivets, minimizing alignment concerns. The analysis here focuses on the alignment in another stacking method, where the daughter board is positioned centrally on the motherboard without pre-fixing with rivets.
The common approach involves adjusting the daughter board’s size and slot on the motherboard to ensure a snug fit, minimizing gaps. However, matching a daughter board of similar size to the motherboard slot often results in excessive offset rather than size compensation issues.
To prevent significant deviation of the PCB daughter board during assembly and ensure consistent and adequate adhesive filling, the gap between the daughter board and motherboard is typically set at 0.15mm. In practical board production, measurements frequently reveal offsets larger than the intended 0.05mm, indicating a 0.1mm offset on certain sides of the daughter boards.
1. Up to 0.1mm on one side. This not only has a greater impact on the conduction between subsequent layers but also affects the bonding force of the daughter-mother board due to insufficient glue in too small spaces. It is evident that the bonding method of the daughter-mother board without clear positioning needs further improvement.
2. PCB Offset Improvement
In practice, PCB manufacturers have attempted to enhance positioning by incorporating concave and convex grooves along the board edge [1], illustrated in Figure 3 below. This design’s advantage lies in its ability to improve the alignment accuracy between mother and daughter boards. However, it still suffers from inadequate glue filling at the corners, posing risks of delamination and bursting.
The positioning of daughter-mother boards still necessitates corner refinement. Clearly, the issue of insufficient glue filling at corners cannot be entirely avoided, but this can be mitigated by new designs aimed at reducing the area of inadequate glue filling at corners, thereby minimizing the risk of delamination and bursting. As depicted in Figure 4 above, the daughter-mother board features rounded corners in the design. Although the board’s overall shape appears largely unchanged, the radius of the corners has been adjusted. In this configuration, the mother board corners have larger radii while the daughter board corners have smaller ones. This design offers dual benefits: firstly, the rounded corner design allows for better glue flow, ensuring more complete corner filling; secondly, it prevents significant corner misalignment after glue flow, thereby aiding in positioning. Simultaneously, rounded corners prevent the complete contact of daughter and mother boards at the edges, allowing adequate space for thorough glue application.
Following the adoption of rounded corners in the daughter-mother board design, experiments involved placing a 0.2mm PCB pad at corresponding positions and drilling 0.2mm through holes. Typically, daughter-mother board offsets are controlled within 2 mils. Furthermore, corner fillet widths of approximately 3 mils ensure complete cross-sectional filling.
Before the PCB daughter board is fully assembled, there are two stacking methods. One method involves securing the daughter board to the edge of the motherboard using rivets, minimizing alignment concerns. The analysis here focuses on the alignment in another stacking method, where the daughter board is positioned centrally on the motherboard without pre-fixing with rivets.
The common approach involves adjusting the daughter board’s size and slot on the motherboard to ensure a snug fit, minimizing gaps. However, matching a daughter board of similar size to the motherboard slot often results in excessive offset rather than size compensation issues.
To prevent significant deviation of the PCB daughter board during assembly and ensure consistent and adequate adhesive filling, the gap between the daughter board and motherboard is typically set at 0.15mm. In practical board production, measurements frequently reveal offsets larger than the intended 0.05mm, indicating a 0.1mm offset on certain sides of the daughter boards.
1. Up to 0.1mm on one side. This not only has a greater impact on the conduction between subsequent layers but also affects the bonding force of the daughter-mother board due to insufficient glue in too small spaces. It is evident that the bonding method of the daughter-mother board without clear positioning needs further improvement.
2. PCB Offset Improvement
In practice, PCB manufacturers have attempted to enhance positioning by incorporating concave and convex grooves along the board edge [1], illustrated in Figure 3 below. This design’s advantage lies in its ability to improve the alignment accuracy between mother and daughter boards. However, it still suffers from inadequate glue filling at the corners, posing risks of delamination and bursting.
The positioning of daughter-mother boards still necessitates corner refinement. Clearly, the issue of insufficient glue filling at corners cannot be entirely avoided, but this can be mitigated by new designs aimed at reducing the area of inadequate glue filling at corners, thereby minimizing the risk of delamination and bursting. As depicted in Figure 4 above, the daughter-mother board features rounded corners in the design. Although the board’s overall shape appears largely unchanged, the radius of the corners has been adjusted. In this configuration, the mother board corners have larger radii while the daughter board corners have smaller ones. This design offers dual benefits: firstly, the rounded corner design allows for better glue flow, ensuring more complete corner filling; secondly, it prevents significant corner misalignment after glue flow, thereby aiding in positioning. Simultaneously, rounded corners prevent the complete contact of daughter and mother boards at the edges, allowing adequate space for thorough glue application.
Following the adoption of rounded corners in the daughter-mother board design, experiments involved placing a 0.2mm PCB pad at corresponding positions and drilling 0.2mm through holes. Typically, daughter-mother board offsets are controlled within 2 mils. Furthermore, corner fillet widths of approximately 3 mils ensure complete cross-sectional filling.
