Flex Circuit Materials Enable Unique Solutions For Flash Memory Circuit Packaging in Next-Generation Cellular Phones
Challenge: Consumer demands for "smart" cellular phones requires ever increasing needs for flash memory and RAM driver circuits in shrinking package space as portable phones continue to miniaturize.
Solution: DuPont Microlux HP adhesiveless roll clad laminate bridges the gap between high performance electrical reliability and unique packaging compatibility to enable low-profile options for critical cellular phone flash memory circuit configurations.
The advantages of flexible circuit technology have long been recognized and incorporated into traditional applications within the aerospace, military, and automotive industries. Within the past several years, however, the explosive growth trend for flex has been toward high-volume consumer applications requiring advanced flash memory and logic circuitry. Cellular phone technology is becoming increasingly reliant on novel IC packaging solutions for high density interconnects (HDI) using thin conductors and dielectrics that provide maximum circuit profile efficiency in the limited “real estate” available in today’s cellular devices. Flash memory demands in cellular phones for such features as cameras, web compatibility, GPS, E-Mail, and spreadsheets is requiring 2X expansion every 2 – 2.5 years even as the overall shell of the portable phone becomes smaller.
With consumers demanding miniaturization AND performance, chip scale package designers looked for options to the reliable but expansive System-On-Chip (SOC) technology to maximize circuit density in the smallest possible “footprint”.
The alternative? Vertical stacking (Z-direction) of multi-chip module components to optimize available package space and interconnect distances. This System-In-Package (SIP) approach can be accomplished with traditional rigid-flex /wire-bonded stacked packages but with limitations to the Z-direction profile and future design flexibility.
An rigid-flex alternative was needed for stacked flash memory packaging that maintained superior performance criteria but allowed an even more compact circuit footprint while maximizing memory and RAM capacity and light weight for cellular “smart” phones.
The solution? A folded stacked adhesiveless flex package using microball grid array processing to attach dies to flex and then a unique flex-forming operation to create a high density, high reliability, and thin profile chip-scale packages.
Materials Selected and Why
A major OEM chose DuPont™ Microlux® HP copper roll-clad laminate as the substrate solution of choice for a high-volume adhesiveless flex fold-over package design for stacked cellular flash memory devices.
Microlux® HP 12/25/12 SS laminate features 25um all-polyimide dielectric as a core for the double sided laminate with 12um low profile ED copper. As supplied in 100 meter standard rolls, HP provided a comprehensive solution to the flash memory and logic circuit requirements by offering a significant Z-axis profile advantage (versus rigid alternative), two-layer adhesiveless performance and reliability, and a flexible packaging option for the required fold-over design to enable optimal circuit density.
As consumer demand for cellular features increases, designers must continue to address high I/O communication needs and rising flash memory/logic specifications. In parallel, they must meet available “real estate” limitations as devices miniaturize and continue to support optimal testing, burn-in, and reliability challenges of next generation designs. Leading mobile phone makers believe solutions like package stacking with DuPont™ Microlux® HP flexible copper clad laminate is the best approach for logic + memory in a customized flex circuit interposer for high-end cellular. This flex-stacked CSP design offers a unique substrate approach to the designer goal of maintaining footprint and pin- out standards for increasingly complex circuit demands while still offering an easily customized package for specific customer logic and memory needs. As such, the flex-based stacked package can quickly adapt to new or next-generation high volume consumer designs.
For emerging “smart phone” technology, flex-based packages similar to this application with DuPont™ Microlux® HP meet a variety of design needs including miniaturization, light weight, high performance, and durability. For next-generation IC package designs such as the “3-D” stacked technology, flexible laminate is expected to play an increasingly vital role in high-volume consumer applications.