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 miniaturization can be achieved by folding the PCB.

Typical applications are found in medical devices (hearing aids, insulin pumps, neurostimulator implants), consumer electronics (mobile phones, portable computers, cameras, TFT displays) or automotive systems (sensor modules, engine control units).

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

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 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
  • 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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