Chip-on-Flex Rework

Flexible substrates are used in 3D connection and mechatronic concepts for reducing the number of connectors needed. They can stand high dynamic bending and are capable of high speed interconnections between different circuit layers. In portable applications, maximum miniaturisation can be achieved by folding the PCB.

Typical applications are consumer electronics (mobile phones, portable computers, cameras, camcorder, TFT displays, …) or sensor modules, engine control units etc. for the automotive industry.

Chip (or Die) on Flex rework is essentially a material handling issue – the flex! Thermal profiles reflect the lower substrate thermal mass as compared to a PCB - typically shorter duration and lower air temperatures to reach liquidus.

Support of the flex circuit necessitates alternate vacuum clamping systems and the use of conductive, rather than convective, lower heating.

Flex Board

What are the challenges?

Incorporating a solution for safe handling and securing of flex substrates
Adapted conductive substrate heating geometry required
Demand on specialized rework equipment with very accurate thermal management

The Finetech Solution

Which Flex Materials Are Used?

Partially flex multilayer PCB
Full flex PCB

High-performance plastic substrates, such as polyimide and PEEK Film
Additionally, flex circuits can be screen printed silver circuits on polyester
The material differs in the combination of use:
- Pure flexible
- Partially flex multilayer

Adapted Heating Plate Rather Than Hot-Air

Heating plate with vacum holder for flex substrates

What heating method is recommended?

“Floppiness” of flex materials prohibits conventional edge clamping methods
Instead, full area bottom side support is required
Full area bottom support prohibits the use of hot air bottom heating (convective)
Instead, conductive heating is required

Mechanical aspects

Vacuum actuated substrate holder for 100% planar and safe fixation of flex materials
Allows uniform contact heating of the whole substrate and prevents warpage of flexible PCB
Flex substrate holders available in different surface shapes and dimensions to meet the specifications of different flex substrates / applications
Integrated carrier with controlled vacuum for die presentation (trays, Gel-Pak^® etc.)

Thermal aspects

Rapid heating, temperature controlled
Special material heating area for minimal thermal expansion
Rapid air cooling
Optional with thermal-independent accuracy for a defined area
Controller optimizable over the whole temperature range
Heating period adjustable in seconds-increments
Inert gas system (optional)

Qualified Tooling

Specialized tooling

Component-specific clamping units
Size and shape adapted soldering heads

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
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}