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

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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
Flash is required!
Preprocessing - underfill cutting with knife tool
Flash is required!
Desoldering the component
Flash is required!
Contactless solder removal
Residual underfill
Residual underfill
Flash is required!
Residual underfill removal
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

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
Operating software for bonding

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
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. This is as easy as process development can get.