As PCB real-estate continues to be in high demand, the RF shield design will remain a challenge to rework. Simply put, the RF shield serves one goal – to minimize Radio Frequency (RF) noise from affecting the sensitive and critical SMD devices beneath the shield. RF shields typically have a unique design and must conform to the layout of the PCB. Because of this, RF shields are not always rectangular or square in design and reworking a shield without disturbing the neighboring components can be challenging.
The Finetech Solution
Adapted Nozzle Design
To remove the shield, the nozzle design must conform to the shield’s external shape. There are strategic points where the shield is soldered to the PCB and the nozzle should be designed so that hot air/process gas is directed to these areas. This ensures that that the shield is consistently removed from the PCB without damage to either PCB or shield. Attempting to remove the shield before the solder reaches melting point can cause damage to the PCB pads, destroying the board.
Solder Removal - Site Dressing
Solder removal can be tricky. Spacing between shield and neighboring components is typically very tight (0.3mm). Removing solder with a soldering iron and wick is possible, but only with the use of high power optics and a steady hand. Instead, this should be done using a contactless method, where a well-controlled volume of hot air/gas is used in conjunction with a vacuum nozzle, thereby avoiding damage to the pads on the PCB.
There are several methods to apply solder. The most common, to dispense solder onto the pads of the area where the new shield will be placed. Another is to dip the new shield into a bath of solder. Each process has advantages and disadvantages:
Advantage: Uniform solder volume
Disadvantage: Time consuming process
Advantage: Simple and quick
Disadvantage: volume of solder can vary
Soldering the New RF-Shield
Alignment of the shield to the pads requires a vision system to overlay both images simultaneously. Re-attaching the shield to the PCB utilizes the same nozzle and a very similar profile to that used in the desoldering process. The only significant change is the addition of a cooling step to solidify the solder paste.
Integrated Process Management (IPM)
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
Recommended Rework Systems
Amongst other factors, the recommended system mainly depends on size and pitch of your component and the required process flexiblity.
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