Via-in-pad (VIP) is a routing technique where a hole is placed directly on the surface-mount component pad.
VIP creates a vertical connection to the inner layers of a PCB. It saves routing space and supports fine-pitch components such as BGAs and QFNs.
Via-in-pad structures are typically filled, planarized, and capped with copper to create a flat, solderable surface. This helps manufacturers to avoid solder wicking during assembly.
IPC-4761 defines the following protection and fill types for VIPs:
- Type VII: Filled and capped via
- Type VI: Filled via without surface cap
The manufacturing process involves drilling and plating the via barrel with copper, followed by filling it with conductive or non-conductive epoxy resin. The surface is then planarized (ground flat) to remove excess resin. A final copper layer is plated over the filled hole to create a flat, solderable surface.
Via-in-pad is widely used in HDI and high-reliability applications, including aerospace, medical, and advanced computing electronics.
Design guidelines for implementing VIP structures in your layout
- Ensure the annular ring width meets the manufacturer’s minimum requirements to prevent tangency or breakouts.
- Have non-solder mask defined (NSMD) pads to enhance solder wetting.
- Ask your fab house to use non-conductive epoxy to maintain CTE compatibility with the laminate. Choose conductive copper fill only when higher thermal or electrical conductivity is required.
- Clearly define fill material, planarization requirements, and copper capping in the fabrication notes.