Underfill

Overview

What is Underfill?

Underfill is an epoxy material that fills gaps between a chip and its carrier or a finished package and the PCB substrate. Underfill protects electronic products from shock, drop, and vibration and reduces the strain on fragile solder connections caused by the difference in thermal expansion between the silicon chip and carrier (two unlike materials). 

In capillary underfill applications, a precise volume of underfill material is dispensed along the side of a chip or package to flow underneath through capillary action, filling air gaps around solder balls that connect chip packages to the PCB or stacked chips in multi-chip packages. No-flow underfill materials, sometimes used for underfilling, are deposited on the substrate before a chip or package is attached and reflowed. Molded underfill is another approach that involves using resin to fill gaps between the chip and substrate.

Without underfill, the life expectancy of a product would be significantly reduced due to the cracking of interconnects. Underfill is applied at the following stages of the manufacturing process to improve reliability.

Wafer and Panel-Level Underfill

Underfill is applied within flip-chip, 2D, 2.5D, 3D, and other packaging architectures at the individual substrate, wafer, and panel-level. Wafer and panel-level applications continue to gain in popularity because they deliver significant cost reductions. Chip-on-wafer (CoW) architecture reduces production costs by continually shrinking and increasing the chip population on wafers, bringing the gap between chips down to a few hundred microns.  At the same time, bump heights underneath the chips are reduced down to tens of microns for small form factors. Despite these tight geometries, large volumes of underfill must be cleanly delivered between chips and flow under them to encapsulate solder bump connections. Precise, consistent, and advanced UPH results are paramount.

Wafer-Level Packaging (WLP) generally encompasses different integration approaches that require underfill, such as fan-in/fan-out, chip-first/chip-last, and a range of other packaging types. WLP is the cornerstone of heterogeneous integration (HI), which includes wafer-level system-in-package (SiP) architectures, 2D, 2.5D, and 3D integrated circuit (IC) stacks, and, most recently, chiplet architecture applications.

WLP 2D, 2.5D, and 3D underfill examples:

Unlike WLP, where packages are produced on round 200 mm or 300 mm wafers, Panel-Level Packaging (PLP) processes and underfills packages on large square panels that accommodate thousands of additional packages.

Board-Level Underfill

At the board level, underfill is applied between finished packages and the PCB. The smaller form factors and the increased component population continue to shrink keep-out-zone (KOZ) dimensions between CSP/BGA and other board components. Dispensing accuracy thus becomes more important to minimize KOZ and deliver underfill fluid as close to the package as possible without landing on top or wicking off to neighboring components. 

Capillary vs. Molded Underfill

Capillary underfill offers important advantages over molded underfill for high-performance computing devices, including CPU, GPU, and AI processors in datacenter, autonomous driving, and mobile devices with AI capability. These devices run under critical situations, and their physical size is large to support their range of functionality and advanced performance. Capillary underfill offers these advantages:

• A long application history and many years of reliability data. With so much field data, it's easier for engineers to manage and control the capillary underfill process to prevent potential reliability issues such as voids.
• Better underfill penetration for larger chips with more complex and large bump layouts.

Get Underfill Application Resources

1. Underfill Volume and Tolerance Calculator – download the handy calculator on this page to determine target dispense volumes based on chip dimensions.

2. Improve Productivity: Jet Underfill into Narrow Gaps Fast – read about underfill challenges, download the Underfill Dispensing for Chip-On-Wafer whitepaper, and watch a wafer-level dispensing video demonstration.

3. ASYMTEK IntelliJet^® Jetting System – download the brochure to learn about the world’s premier high-frequency jet for achieving consistent, precise dispensing of a wide variety of fluids, with ultra-fast jetting speeds up to 1.8 million dots per hour and a maximum frequency of 1000 Hz, ideal for narrow gap jetting.

ASYMTEK Product Solutions

The ASYMTEK Vantage^® and Forte^® Series dispensing platforms offer advanced productivity and precision with dual-valve IntelliJet Jetting and advanced process controls. Our Spectrum^® ll fluid dispensing system has been the tool of record for high-volume fan-out WLP at the world’s largest semiconductor factory for the past several years, as shown at 2:03 in the following BBC Click interview.  ASYMTEK system capabilities such as Fids-on-the-Fly, Continuous Path Motion Control, and patented Calibrated Process Jetting (CPJ) ensure fast fiducial finding, consistent dispense volumes, and continuous speed and direction to increase throughput. 

Are you researching equipment upgrade options for your underfill application? Check out the Upgrading from the Spectrum ll to a Forte Series Dispensing Solution case study for details about enhanced dispensing software, dual-valve jetting, and 1.5G acceleration that takes underfill UPH well beyond what's possible with older dispensing platforms and software.

Supporting a Range of Underfill Applications

• System-in-Package (SiP)
• Integrated Passive Device (IPD)
• Redistribution Layer (RDL)
• Chip-on-Wafer (CoW)
• Chip-on-Wafer-on-Substrate (CoWos)
• Package-on-Package (PoP)
• Fan-Out Wafer Level Packaging (FOWLP)
• PCB/Flex circuit
• Organic substrate
• Ball Grid Array (BGA)
• Chip Scale Package (CSP)
• Flip-chip
• Controlled Collapse Chip Connection (C4)
• Edge or corner bond partial underfill
• No-flow underfill and jetting encapsulation

Related Products

• Vantage Series single- or dual-valve
• Forte Series
• ForteMAX dual-valve
• Spectrum
• IntelliJet Jetting System
• ReadiSet^® Jet Cartridge
• Calibrated Process Jetting (CPJ)
  
• Fids-on-the-Fly
• Continuous Path Motion Control
• Canvas® Software
• Fluidmove® Software

Why Nordson?

You can be confident when choosing Nordson as your fluid dispensing partner. Our commitment to innovation, quality, and customer service excellence allows us to consistently deliver high-performing, long-warranty, and reliable systems and valves. We’ve gained more than 30 years of experience supporting the world’s largest electronics manufactures. When you work with Nordson, you’ll have access to sales, service, and applications expertise in locations around the globe, including the Americas, Asia Pacific, and EMEA.