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!

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
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}