Blind PCBs

Blind PCBs are non-through vias that connect the outer layers of a circuit board to inner layers without through out the entire board.

 

The industry generally uses laser drilling technology to manufacture printed circuit boards with blind hole designs. When customers have high requirements for pressure resistance, the dielectric layer of the blind hole layer needs to be relatively thick, or the blind hole needs to withstand large currents, the conventional HDI may not meet the customer's design requirements. In this case, the mechanical blind hole design method is a better choice. For the manufacture of mechanical blind hole printed circuit boards, the industry commonly uses a processing method of first making through-holes in the blind hole layer, and then filling the blind holes with resin plugs to prevent poor filling of the blind holes. Next, the inner layer circuit layer is made, and then the layers are laminated and pressed together. Finally, the outer layer is processed similarly to the conventional multi-layer board process.

 

By optimizing the design and using semi-cured film filling technology instead of resin plug hole technology under fixed lamination conditions, the process can be simplified, efficiency can be improved, and costs can be reduced. Specifically, the following design optimizations are recommended: (1) for mechanical blind vias in FR-4 material, use semi-cured film with higher resin content, with a quantity of more than 2 sheets; (2) the thickness of the mechanical blind via layer should be less than 0.3mm; (3) the mechanical blind via hole size should be designed at (0.2~0.4)mm.

 

 

However, Design modifications for the mechanical blind hole process must be confirmed and certified by the customer to prevent reliability issues: (1) If modifications to the press stack structure or mechanical blind hole diameter do not conform to the customer's design, the customer should be consulted and the modifications can only be made after the customer has evaluated and confirmed them based on factors such as current flow through the blind holes, voltage resistance, and signal effects. (2) The filling capacity of the mechanical blind hole product can be adjusted and tested according to the actual situation of each company to further improve the filling process.

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