Circuit Board Repair Guide > BGA Component Rework Procedures > 9.3.1 Hot Gas Method for Eutectic Solder Ball BGA Rework

Hot Gas Method for Eutectic Solder Ball BGA Rework

Repair Circuit Boards | Repair SMT Pads | Repair BGA Pads | Repair Lands | Repair Edge Contacts
Repair a Conductor | Plated Hole Repair | Base Board Repair | Replace Solder Mask or Coatings

This procedure covers the most commonly used methods for replacing Plastic Ball Grid Array (PBGA) components and Ceramic Ball Grid Array (CBGA) components. These packages are typically referred to as Plastic Ball Grid Array (PBGA) or Tape Ball Grid Array (TBGA) or Chip Scale Package (CSP) components.

Caution - Operator Safety
A thorough review of the equipment manual and comprehensive training are mandatory. Daily maintenance is essential. Consult the equipment manual for more information.

Caution - Component Sensitivity
This method may subject the component to extreme temperatures. Evaluate the component's tolerance to heat prior to using this method.

Caution - Circuit Board Sensitivity
PC Boards are made from a great variety of materials. When subjected to the high temperatures they are susceptible to the following types of damage:

1. Layer delamination.
2. Copper delamination, separation of pads, barrels of inner layers.
3. Burns and solder mask chipping.
4. Warp.

Each circuit board must be treated individually and scrutinized carefully for its reaction to heat. If a series of circuit boards are to be reworked, the first several should be handled with extreme care until a reliable procedure is established.

Related Procedure References
CTC 1.0 Foreword - Circuit Board Repair Guide
CTC 2.1 Handling Electronic Assemblies
CTC 2.2.1 How to Clean a Circuit Board
CTC 2.2.2 Cleaning Circuit Boards, Aqueous Batch Process
CTC 2.5 Baking and Preheating of Printed Circuit Boards
CTC 7.1.1 Quality Soldering Basics
CTC 7.1.2 Preparing Circuit Boards and Soldering Tools for Soldering and Component Removal

Tools and Materials
BGA Specific Nozzle Microscope
Cleaner Oven
Cleaning Wipes Soldering Station
Flux, Liquid Solder
Hot Air Rework Station Thermocouples
Hand Held Digital Thermometer Vacuum Pen
Tape, Kapton  

Printed Board Type: R/F/W/C  |  Skill Level: Advanced  |  Conformance Level: High  |  Rev.: Pending  |  Date: Pending

Commercially available BGA rework station

Figure 1: Commercially available BGA Rework Station.


General Notes
   
1. 
Profiles for both removal and replacement of the selected component must be developed prior to rework. (See section 8.5.2 for instruction).
   
2. 
Check the board for any heat sensitive components that may be damaged by the process, especially near the location of rework.
   
3. 
Profiles are board and site specific. Profiles that are successful on one board type are not necessarily effective on other assemblies.
   
Removal Procedure
   
1.  Select the appropriate nozzle and install into the rework station.
   
2.
The nozzle should hold the component securely yet allow for expansion during the process. Custom nozzles may need to be fabricated.
   
 
Note
Nozzle to part fit is multidimensional. Closely observe the component ball location relative to the nozzle bottom. Whether the balls protrude or are deeply recessed into the nozzle may affect part positioning during reflow.
   
 
Note
Pre bake the board to drive out accumulated moisture. The length of pre bake will be affected by the board's environmental exposure. A pre bake temperature of 75 °C to 100 °C is recommended.
   
3.  Place a pre baked board onto the fixture.
   
4.  Attach a monitoring and trigger thermocouples.
   
5. 
Establish a bottom side, under part threshold temperature from which to begin the reflow ramp. 140°C underneath the part should correspond to approximately 90°C at 2" from the nozzle on the board's top side. Choosing a starting point in this approximate temperature range will help to reduce localized warping during BGA ball reflow.
   
 
Note
Anti static fixture material may be used when coplanarity problems exist as the circuit board expands above its glass transition temperature (Tg).
   
6. 
Apply a small amount of liquid flux to all leads of the component. A syringe may be used to inject flux under the device.
   
7.  Align the device and nozzle.
   
8. 
Activate the desoldering profile and monitor the board temperature using the hand held digital thermometer or other appropriate monitoring device.
   
 
Note
If the bottom temperature exceeds 200°C, terminate the removal process and check the process parameters.
   
9. 
Lift the nozzle when reflow temperatures are reached. A vacuum pen may be used to remove the part if a vacuum tip is not incorporated into the nozzle itself.
   
10. Clean the area. Remove all flux residue from the site.
   
Surface Preparation
   
 
Note
This procedure uses eutectic solder alloy bumps to prepare BGA pads for combination with BGA part balls.
   
1. 
Remove all excess solder from the site (See section 7.1.2 Preparation for Soldering).
   
2.  Clean the area.
   
3. 
Inspect all pads for damage. It is critical that solder mask is not disturbed between the pad and its via. Solder volume problems may exist if solder is allowed to escape down the vias.
   
4.  Apply liquid flux to the pads.
   
5. 
Apply new eutectic solder in consistent bumps to each BGA pad. The bump angle, surface to pad, should be between 30° and 45°.
   
Replacement
   
1.  Select the appropriate nozzle and install into the rework station.
   
2. 
The nozzle should hold the component securely yet allow for expansion during the process.
   
 
Note
Pre bake the board to drive out accumulated moisture. The length of pre bake will be affected by the board's environmental exposure. A pre bake temperature of 75 °C to 100 °C is recommended.
   
 
Note
To remove moisture from components, it is recommended that all parts are baked per the component manufactures suggestion. Generally, a 24 hour bake at 125°C will remove most moisture. This will prevent pop-corning or delamination of the component.
   
3.  Place a pre baked board into the fixture.
   
4.  Attach monitoring and trigger thermocouples.
   
5. 
Establish a bottom side, under part threshold temperature from which to begin the reflow ramp. 140°C underneath the part should correspond to approximately 90°C at 2" from the nozzle on the board's top side. Choosing a starting point in this approximate temperature range will help to reduce localized warping at BGA ball reflow temperature.
   
6.  Align the device and nozzle.
   
 
Note
If the bottom temperature exceeds 210°C, terminate the replacement and check the process parameters.
   
7.  Lift the nozzle when well below reflow temperatures.
   
8.  Ion fans may be used to cool the components and the board.
   
9.  Clean the area. Remove all flux residue from the site.
   
X-ray inspection verifies shorted spheres

Figure 2: X-ray inspection verifies
shorted spheres.
Evaluation
   
1. 
Visual examination of the perimeter spheres for joint shape, alignment and condition.
   
2.  Visual examination for part planarity and condition.
   
3.  X-ray examination as required for shorting or joint deformities. (See Figure 2).
   
4.  Electrical tests as applicable
   
5.  On removed part, visual evaluation of post reflow condition.




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