Using Blind, Buried, and Stacked Vias
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HDI Structures
Using Blind, Buried, and Stacked Vias on Complex Designs
Incorporating High Density Interconnect (HDI) structures is commonly utilized on advanced designs as a way to overcome space issues resulting from high I/O, fine pitch components. To achieve the density required in HDI designs, line width, spacing, hole diameters and pad sizes must all shrink. Reducing copper foil thickness on inner layers, reducing dielectric spacing to maintain low drill aspect ratios, incorporating via-in-pad and specifying the correct copper wrap are all critical factors in a successful design. However, for the most reliable structures, maintaining the following design guidelines will have the best results.
- Limit stacking of micro vias to 2-stack, if more than 2 stacked layers are required, stagger via layers
- Never stack microvias on top of buried vias
- Maintain a 6 mil micro via diameter, with a 12 mil capture pad
- Maintain an aspect ratio of .75:1 or less for microvias
- Specify .0002” copper wrap in the starting foil
- Copper fill microvias
- Design a D coupon that represents all via structures that can be tested for reliability using OM testing
Summit’s preferred method of testing HDI reliability is with OM testing.
Technology Insights
Our teams have been manufacturing PCB's for more than 30 years. Here are some of the best practice guidelines and design resources to assist you in the design process.
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Summit Interconnect is one of the leading providers of complex, rigid, and flexible printed circuit boards in North America, offering solutions ranging from advanced prototyping to high mix, low-to-mid volume production. Summit serves customers across the aerospace, defense, and other highly demanding commercial sectors and has facilities in California, Illinois, and Toronto, Canada. Summit is a recognized industry leader in quick-turn manufacturing and has expertise with a wide range of materials like high-speed digital, RF/microwave, and mixed constructions.