Choose the right advanced packaging methodology for metal fill rules
Advanced packaging design comes with a wide of foundry and OSAT requirements. A new white paper describes three strategies that can be used to satisfy these needs while also ensuring that the specification is adhered to as closely as the foundry/OSAT rules.
In ‘A Proven Methodology to Meet Manufacturing Process Requirements for Metal-Filled Areas and Planes’, author Kendall Hiles, a Senior Product Specialist with Siemens EDA, explains why suppliers have such stringent demands.
“Their strict metal fill requirements address two main issues,” he writes. “The dielectric and metal layers can be very thin, 15 µm or less, and during the build-up and RDL process they can suffer from areas of delamina[1]tion due to trapped pockets of gas. Think of it being like adding a screen protector to your smartphone and how hard it is to get the air bubbles out. Also, uneven conductor densities on the same layer or across layer pairs can cause warpage in the package and/or the wafer.”
The types of design that are particularly susceptible to these issues for metal areas and planes include such advanced packaging formats as interposers, high-density-fan-out wafer level packages and high pin-count flip-chip ball grid arrays.
Hiles describes how to implement three different methodologies to satisfy these needs.
- Dynamic Hatched Filled Metal Areas – a simpler technique that should be applied early in the design.
- Outgassing Voids – a common post-processing technique that enables power and signal integrity to be addressed alongside DFM requirements.
- Dummy Metal Fill – a technique particularly useful on interposer projects with high-bandwidth memory or omni-directional interconnects.
All three are illustrated and summarized with reference to the types of tool that aid implementation and can provide automated guidance to further reduce design time for advanced packaging.
“The key is choosing the methodology that best meets vendor rules, meets your power delivery network specifications, allows rapid engineering change order turns, and is repeatable,” Hiles observes.
