What's Blind and Buried Vias/Via-In-Pad?
A via interconnect hole that resides in a solderable pad, where the requirements are for a flat, planar surface that does not contribute negatively to the placement or orientation of the soldered component.
Common Method of Creating Via-In-Pad
- Using mechanical drills, the via spans one or several dielectrics and conductive layers, and is filled (post-plating) with a conductive or non-conductive epoxy material that is void-free and facilitates a planar surface to create the surface pad that a device will be soldered to.
- Using laser ablation, the micro via spans a single dielectric and connects the surface layer to the next layer down in the stackup (except variable-depth micro vias). The subsequent micro via is fully copper plated and planarized to create a flat surface pad that a device will be soldered to.
- TYPE I (1 + n + 1) - Laser micro vias on both sides of the board.
- TYPE II (1 + n +1) - Laser micro vias on both sides of the board, with buried vias in the core.
- TYPE III ( 2 + n + 2) – Laser micro vias on both sides of the board, may have buried vias in the core.
Via Fill Materials
Conductive (Type: Silver Coated Copper Particulates):
- DuPont CB-100
- Tatsuta AE3030
- San-Ei Kagaku PHP-900 IR10F
- Peters PP2795
Best in class overall end-user performance with San-Ei IR-10F product.
Very high copper peel strength.
Low CTE above tg of the laminate material.
Excellent performance at elevated temperatures.
Note: Non-conductive CTE is comparable to FR4 material. It is preferred to use non-conductive via fill unless thermal conductivity is the requirement. Filled via drilled sizes: Smallest .008 Largest .020
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You can trust Advanced Circuits to provide in-depth information on this and many more subjects relating to the manufacture and assembly of printed circuit boards. Find out more about High Performance Materials for Advanced Designs in our Tech Talk for Techies report. It discusses materials that provide greater thermal performance and severe environment reliability. Click Here to see Part 2 of the report.