QFN Rework

Flat packages such as QFNs (Quad Flat No-lead) or other MLFs (Micro Lead Frame) with outstanding thermal, inductive and capacitive characteristics (for example resulting in much shorter reaction times) are being increasingly incorporated into densely populated, space-saving assemblies. Unlike BGA components, QFNs however do not provide a solder ball array for SMD assembly but have to be soldered to the assembly with their contact pads attached directly to the metalized body (lead frames). This technology makes much higher demands compared to the handling of standard SMD components.

  • QFN component
  • View on QFN component with process camera
  • QFN x-ray inspection...1. uneven solder allocation
  • QFN x-ray inspection...2. uniform solder allocation with direct component printing

What are the Challenges?

  • Find a manual QFN rework solution without limiting rework yields
  • Restrict the rework process to one reflow process to have reworked QFN in OEM quality
  • Work on densely populated boards with confined working areas where conventional solder pasting methods (stencil and blade) are not viable
  • Method for direct component printing of solder paste required
  • Make sure the paste printing method minimizes solder voids according to IPC/JEDEC
  • Avoid accuracy issues aligning the paste printing stencil to LAN array and the component to the substrate (two potential sources of errors)
  • Consider enhanced heat flow from component to PCB (QFN on heatsink) which requires particular attention when establishing heating profiles and choosing rework tooling

The Finetech Solution

Direct Component Printing

  • QFN after removal
  • Direct Component Printing Module
  • Applying solder paste with spatula
  • Precise paste printing result
  • Direct component printing is a very effective, uncomplicated and time-saving method to improve QFN or other MLF rework yield
  • Paste application as part of the rework cycle can be performed within any rework system equipped with the Direct Component Printing Module
  • No second reflow process necessary (i.e. solder reflow from transfer plate): helps avoiding accuracy issues and thermal stress issues
  • Applicable for volume rework of QFN or other MLF components with fine pitch
  • Component-specific printing stencils for maximum flexibility
  • QFN rework in OEM quality!

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).

Optical Precision Alignment

  • Overlay image of QFN and nozzle
  • Video optics for precision positioning and alignment
  • Equipped with autofocus and autozoom function
  • Zoom position and adjustment of lighting are saved together with the soldering profile for each individual component on a PCB (camera will automatically operate at optimal magnification and proper lighting intensity, any optical adjustment is fully operator independent)
  • Viewing components within a large size range without any adjustment directly at the camera
  • For significantly enhanced workflow

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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