In this paper, we review the three methodologies commonly used to achieve foundry/OSAT requirements for metal-filled areas and planes in advanced package designs: dynamic hatched-filled metal areas, outgassing voids, and dummy metal fill. The key is choosing the methodology that best meets vendor rules, meets your PDN specifications, allows rapid ECO turns, and is repeatable.
Often designers are amazed at the diversity of requirements fabricators and manufacturers have for metal-filled areas and planes in advanced package designs. Package fabricators and manufacturers do not like solid metal planes or large metal areas. Their strict metal fill requirements address two main issues. 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 delamination 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 combination of these issues makes the designer’s job of meeting the manufacturing rules a challenge. Further, the diversity of substrate technologies from numerous vendors means there’s no one-size-fits-all solution. In this paper, we will walk through three methodologies that are commonly utilized on advanced package designs:
- Dynamic hatched-filled metal areas
- Outgassing voids
- Dummy metal fill
These are the most common methods to achieve foundry/OSAT requirements for metal-filled areas and planes in advanced package designs such as interposers, high density-fan-out wafer-level package (HDFOWLP), and high pin count flip chip BGAs, so it is important to understand how to use them.
In summary, dynamic hatched fill, outgassing voids, and dummy metal fill are the most common methods to achieve foundry/OSAT requirements for metal-filled areas and planes. The key is choosing the methodology that best meets vendor rules, meets your PDN specifications, allows rapid ECO turns, and is repeatable. To expedite verification, make sure you turn on dynamic cross-probing between the vendor sign-off tool and the layout tool.
