Package on Package (PoP) Rework

Package on Package (PoP) is an IC-packaging technology with vertical combined logic and memory components where two or more BGAs (Ball Grid Arrays) are stacked. Normally the discrete logic is located in the bottom with a memory device on top of it. Because of the high package density, these components are very important for the communication technology (handset makers etc.).

Beside an intelligent combination of bottom and top heating providing precise thermal management, a special nozzle design is required to pick up those components during rework.

PoP component on a PCB
Principle of a flip chip PoP component
Cross section of a PoP component

What are the Challenges?

The PoP rework process is similar to standard BGA rework, but because of the vertical assembly, a special clamping solution is necessary. PoP packaging involves the following specific challenges:

High-count fine ball pitch (<0,65 mm)
Reflow simultaneously on the PCB
Applying a sufficient clamping force to lift the component out of liquid solder without lateral movement
Reworking different component heights
Avoid disturbing neighboring components on densely populated boards
Amount of warpage for each package must be limited
Precise force control during stacking to avoid shifting of already placed package levels

The Finetech Solution

Remove, Clean, Replace

De-soldering a PoP component
Soldering a PoP component

Preheating the PCB
Desoldering the PoP component without affecting neighbored components by using software controlled heating units and qualified tooling
Pick up the component with Finetech’s special vacuum activated tweezers
Removing residual solder material contactless to avoid any stress to the solder pads
Pick up, flux-dip and precise alignment of each package
In a final step, simultaneous reflow of all interconnections; packages and PCB

Special Nozzle Design for Quick and Safe Rework

Clamping nozzle with actuated tweezers in small clearance between PoP and small passives
Front view on nozzle tip

Specific nozzle with vacuum controlled tweezers for de-soldering and soldering
Nozzle can be adapted easily to different component heights by turning one screw
Thin and specially shaped tweezers to clamp the component on every stack level
Tweezers distance easily adjustable for rework on densely populated PCBs even in clearance of 0.3 mm to adjacent components
Synchronic tweezers actuation is freely software programmable to avoid any stress to non-molten solder joints

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}