Underfill Rework

Underfilled components are used in consumer electronic products (mobile devices, portable computers etc.), in the automotive industry (sensor modules, engine control units etc.) or whenever flip chips are incorporated in products with maximum miniaturization.

An underfilled chip contributes to an improved overall product quality, offering higher reliability and better lifetime. The underfill material provides protection against humidity, thermal stress and all kinds of mechanical impact.

Reworking components with rework-able underfill is applicable if the components or substrates are expensive, hard to obtain or if complete products need to be saved.

  • Underfill component

What are the challenges?

  • Avoid disturbance of  neighboured components on small-sized (pitch down to 400 µm or below) high-density SMD assemblies with distance down to 300 µm
  • Process fluctuations during production result in undefined fillet shapes
  • Avoid thermal and mechanical stress to the surface top metal layer and solder resist
  • Find the appropriate process according to the specific underfill material
  • Variable stack heights require adaptive tooling and specialized rework equipment

The Finetech Solution

Various Underfill Materials

The appropriate rework process is mainly determined by the underfill material. There are various expoxy based underfill materials differing in the composition and characteristics:

  • Hard or flexible
  • Expansion ability
  • Curing temperature
  • Removal temperature
  • Purely mechanical or chemical underfill removal

Typical Underfill Rework Process

  • Preprocessing - underfill cutting with knife tool
  • Residual underfill
  • Residual underfill
  • Clean site after underfill removal

The whole rework process consists of the following steps:

  • Preprocessing of the component, if necessary (cut underfill to avoid lifting neighboured components)
  • Desoldering using a clamping tool
  • Solder removal
  • Residual underfill removal using heat, brush and chemical solvent
  • Soldering of new component
  • Underfilling and curing

Controlled Mixed Soldering System

  • Flash is required!

  • Controlled Mixed Soldering System

Finetech’s unique thermal management concept uses “cold” air or gas (typically nitrogen) introduced into the hot-gas stream in a mixing chamber. The chamber location is just before the air passes through the nozzle onto the component. This gas mixture results in a highly responsive system - reducing over and under-shoot to barely perceptible levels. Tracking of the pre-set temperature is optimized and when combined with mass-flow-control of gas volumes (up to 70L/min), produces an effective heat delivery system. Heater lifetime is also increased and system-to-system reproducibility is greatly enhanced (±2ºC).

Adapted Tooling

  • Tools needed for underfill rework

Highly precise clamping tool with vacuum support for secure handling

  • Designed to compensate thermal expansion effects
  • Provides very localized top heat input to avoid disturbance of neighboured components
  • Inert gas support provides process atmosphere adequate to reflow oven conditions
  • Tool design allows access to densely assembled components with small clearance

Variable knife for fillet cutting
Q-tip, ESD brush, chemical solvent

Integrated Process Management (IPM)

  • Integrated Process Management (IPM)
  • Principle of process gas integration
  • Operating software for rework

The Integrated Process Management (IPM) is the center piece of a FINEPLACER® system1 - the place where it all comes together. IPM is more than just thermal management. It synchronizes the control of all process modules and their related parameters:

  • Controlled and precisely balanced interaction of top and bottom (pre-)heating and cooling
  • Control of temperature, time, force, power, energy, flow
  • Process-integrated camera and light control
  • Controlled process gas integration for reduced solder contamination, minimized surface tension effects and smooth spherical solder residues

 IPM is very complex, yet easy to access. Via the GUI of the operating software, the user has perfect control of all required adjustments. Just drag 'n drop to define temperature ramps or activate process modules. All settings are represented in only one profile, making for a very intuitive work flow.
 
The operating software provides an ever-growing library of profiles for all kinds of processes. It also offers comprehensive data logging functions essential for statistical process control.

In combination with the system-to-system process transfer capability this is as easy as process development can get.

1 FINEPLACER® core offers co-ordinated top and bottom heating but does not support IPM

FINEPLACER® Rework Systems

  • FINEPLACER® coreplus
    Rework of medium-sized boards
  • FINEPLACER® matrix rs
    Future in advanced rework
  • FINEPLACER® pico rs
    High density rework station
  • FINEPLACER® micro rs
    Hot air SMD rework station
  • FINEPLACER® micro hvr
    High volume rework station

Amongst other factors, the recommended system mainly depends on size and pitch of your component and the required process flexiblity.

Browse our product range or get in contact with your sales contact to figure out the best equipment solution for your needs.

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