Circuit Board Repair Guide > BGA Component Rework Procedures > 9.2.2 Development of a BGA Component Rework Profile Using the Smart Track Method

Development of a BGA Component Rework Profile Using the Smart Track Method

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 development of thermal profiles for BGA component removal and replacement using the Air-Vac Smart Track BGA Rework System. The procedure will automatically develop an optimized profile.

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
 
Man working at BGA rework station
Ball Grid Array Rework Station

Tools and Materials
Aluminum Foil Profile Development Circuit Board Assembly
BGA Rework Nozzles Profile Development BGA Components
BGA Rework System (Air-Vac) Tape, Kapton
Cleaner Tape, High Temperature Masking
Cleaning Wipes Thermal Adhesive (J-B Weld)
Microscope Thermometer, Digital
Oven  

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. Plastic BGA's are especially sensitive to moisture absorption. Carefully evaluate pre bake requirements.

Caution - Circuit Board Sensitivity
Circuit boards are fabricated from a wide 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.

Printed Board Type: R  |  Skill Level: Expert  |  Conformance Level: High

1.0 Overview

This procedure automatically creates a thermal profile based on user-defined target parameters. These may include; board temperature, soak duration, BGA package temperature, BGA package ramp rate, solder joint temperature, and time over reflow. The Smart Track profile development method is non-destructive since drilling holes to embed Thermocouples is eliminated. However, profile development circuit boards may be subjected to multiple thermal cycles. The Smart Track method automatically adjustments heater temperature, gas flow rates, and duration on a real-time basis. The method uses an automatic repetition procedure, using information learned from previous runs to optimize the process.

Note
Read and understand all instructions that accompany each project prior to starting.

Note
Prior to starting the profile development process both the BGA Rework machine and the circuit board should be at, or near, room temperature. Avoid the use of fans to cool the circuit board or BGA rework machine during Profile Development. Doing so may interfere with the software program. Allow the circuit board and BGA rework machine to cool naturally.

Note
Profiles developed on one Air-Vac machine are portable, and may be transferred to other Air-Vac machines.

Note
If the circuit board has multiple BGA component locations that require profiles, and all the BGA components are the same type and size, one rework profile may be used for all. The BGA component location to select for the profile should be the one that will generally be the most challenging to rework. The most difficult BGA components to rework will generally be:
1. Closest to the edge of the circuit board.
2. In the most densely populated area.
3. Near, or surrounded by, a ground plane.
2.0 Initial Setup
  1. Select the BGA Rework Nozzle that will be used to develop the BGA Rework Profile. Nozzle Part Number should correspond to BGA physical size. Test fit Nozzle. Nozzle should fit over BGA component with minimal gap.

    Record Nozzle Part Number, BGA Component Height, and Circuit Board Thickness on BGA Rework Process Worksheet.
    Nozzle Styles

    EZ & DVG Style Nozzles
    Not package specific. Zero adjacent component clearance. Adjacent components within .300" may reflow.

    X & M Style Nozzles
    Component-specific design. 4-sided exhaust ports minimize adjacent component temperatures. Anti-crushing feature. Adjacent component clearance X=.100", M=.032".

    ACG Style Nozzles
    Component-specific design. Oversized heating tube optimizes thermal performance. Torlon corner standoff eliminates placement height concerns. Adjacent component clearance=.200". Also available with .100" clearance.

    Note
    Depending on the BGA Nozzle type, the epoxy that secures the Thermocouple to the top of the BGA component to be profiled may prevent the BGA Nozzle from contacting the circuit board surface.


  2. Test all Thermocouples prior to each use using a Digital Thermometer.


  3. Test fit the the circuit board on the base of the BGA rework machine. Consider the following:
    1. The need to remove components or other hardware to allow the location to fit under the nozzle without interference. If component need to be removed see appropriate procedure. Properly label removed components so that they can be replaced.

    2. Need to apply "heat shields" using Kapton tape or aluminum foil.

    3. Location of placement of Thermocouples.
Thermocouple on BGA component

Figure 1: Place tip of Thermocouple
#2 on center of the BGA component. Secure with Thermal Adhesive.


4.  
Clean the top of the BGA component to be profiled. Place the tip of Thermocouple #2 on the center of the BGA component. Apply High Temperature Tape to temporarily hold the Thermocouple in position. Tape should not cover the tip of the Thermocouple. (See Figure 1).
 
5.  
Mix up a small amount of Thermal Adhesive. Stir for one minute to insure a complete mix. Apply a small dab, (approx. 1/4" in diameter) to secure Thermocouple tip to BGA top. Place the circuit board in an oven for 15 to 30 minutes at 160° - 175°F ( °C) to cure the Adhesive. After Adhesive cures remove from oven and allow to cool. (See Figure 1).
Place thermocouples under BGA profile component

Figure 2: Place Thermocouple #3,
and #4 under opposite corners of
the BGA Profile component. Place Thermocouple #5 under adjacent component. Secure Thermocouples
the circuit board surface using High Temperature Tape.


6.  
Place Thermocouple #3 under one corner of the BGA component. Place Thermocouple #4 under the opposite corner of the BGA component. Thermocouples should be inserted far enough so that the wire insulation is just under the BGA component. Optimum location for these Thermocouples is between the 2nd and 3rd row of BGA solder balls. If needed, check location of Thermocouples using a microscope. Secure Thermocouples the circuit board surface using High Temperature Tape. (See Figure 2).

Note
The corners selected should be those closest to adjacent components or ground plane areas.
 
7.  
Place Thermocouple #5 under corner of adjacent component. Secure Thermocouple the circuit board surface using High Temperature Tape. Apply High Temperature Tape to divert hot air from BGA Rework Nozzle from flowing directly onto Thermocouple.
 
8.  
Place one Thermocouple (#6) directly under the center of the BGA component on the opposite side of the circuit board directly in contact with the circuit board surface. Secure Thermocouple the circuit board surface using High Temperature Masking Tape.
Table 1 - Thermocouple Locations

Number Thermocouple Location
1 IR Sensor
2 Top center of BGA component to be profiled. 
3 Corner location under BGA component to be profiled.
4 Opposite corner location under BGA component to be profiled.
5 Under adjacent component. 
6 Bottom side of circuit board under center of BGA component to be profiled.


Support area around BGA component to be profiled

Figure 3: Place supports under
circuit board to support area around BGA Component to be profiled.


3.0 Profile Development Setup
 
1.  
Place the circuit board on the base of the BGA rework machine. Circuit board should be centered over the bottom heater. Clamp circuit board in place using built-in machine clamps.
 
2.  
If needed, remove tape previously placed on the top of the BGA component to be profiled.
 
3.  
Plug in the Thermocouples as shown in Table 1 - Thermocouple Locations.
 
4.  
Install BGA Rework Nozzle in BGA Rework Machine. Depending on the nozzle type, the epoxy securing the Thermocouple to the top of the BGA component may prevent the nozzle from contacting the circuit board surface.
 
5.  
Position circuit board so that BGA component to be profiled is aligned below nozzle. Fine adjust X, Y and theta positions and lock the machine base.
 
6.  
Lift Board Carrier and place supports under circuit board to support area around BGA Component to be profiled. Check to be sure supports contact circuit board surface, not components. Lower Board Carrier. (See Figure 3).
 
BGA component being profiled

Figure 4: Position the IR Sensor Thermocouple #1 approx. 2" from
edge of BGA component being
profiled.


7.  
Position the IR Sensor Thermocouple #1 approx. 2" from edge of BGA component being profiled. Sensor should be above a spot on circuit board surface free of components. IR Sensor averages the surface temperature over a 3" circle. (See Figure 4).
 
8.  
Power on the machine. Pass "operator registration" and "password log in" screens.
 
9.  
Select "Control" - "Thermal Smart Track" - "Auto Temperature Profiling". The Thermal Smart Track screen appears. The system will automatically initialize the process parameters (user-adjustable) to the default (standard) settings. These factory settings represent a good starting point to begin the profile. If needed, the system will make adjustments automatically during the "optimize" cycles.

Note
Prior to starting the profile development process both the BGA Rework machine and the circuit board should be at, or near, room temperature. Avoid the use of fans to cool the circuit board or BGA rework machine during Profile Development. Doing so may interfere with the software program. Allow the circuit board and BGA rework machine to cool naturally.
 
10. 
Enter the following information onto the screen. Values may vary depending on the application.
 
Table 2 ° Cycle Parameters

Parameter Standard Value
Device Joint(s) Average - Target (°C) 200°C
Device Joint(s) Average - Cool Down (°C) 160°C
Device Joint(s) Average - Reflow (s) 060 seconds
Min. Soak (°C) 140°C
Max. Soak (°C) 170°C
Soak (s) 060 seconds
T/C - Highlight Thermocouples being used.
Device Top T/C #2 - Max (°C) 230°C 
Device Top T/C #2 - f(x) 2
Board Control T/C #1 - Target (°C) 090°C
Board Control T/C #1 - Start (°C) 065°C
Board Control T/C #1 - Max (°C) 130°C
Adjacent Device(s) Independent - Max (°C) 180°C Normally T/C #5
Nozzle Control Flow (%) Set by selecting Nozzle Part No.
Nozzle Control Preheat (°C) 125
Device Top Ramp (°C/s) 1.0

4.0 Profile Development Operation
 
1.  
Recheck the values are entered into the "Automatic Temperature Profiling" screen.
 
2.  
In the Options section, Click the "Cycle Start/Stop" icon to start the Automatic Temperature Profiling cycle.
 
3.  
If Automatic Temperature Profiling cycle fails to start, follow the "Pop-Up" instructions.
 
4.  
Monitor the process and stop the system if the Board Control T/C #1 temperature exceeds 183°C.

You can monitor various stages by observing the following indicators:

Board - This stage ends when the Board Control Target temperature is reached.

Preheat - This stage ends when the PCB Target temp. of the Board Control is reached.

Soak - This stage ends when the Soak Seconds value of the Device Joints is reached.

Reflow - This stage ends when the Reflow Seconds value of the Device Joints is reached.

Cool Down - This stage ends when the solder joints are under 183°C.
 
5.  
If all of the Thermal Profile Parameters have been met on the first pass "Done" indicator will be illuminated. Proceed to section 5.0 Profile Saving.
 
6.  
If all of the thermal profile parameters have not been met on the first pass the "Optimize" indicator will be illuminated.

Note
The system will automatically run up to 3 additional cycles. Do not Start or Stop the machine, nor make any parameter changes. System will restart another cycle once the circuit board has cooled down to the Board Control T/C #1 Start Temperature.

The following Process Optimization Rules may be applied during the Optimize cycles. Only one rule can be applied per optimize cycle.

001
The targeted device joint average temperature was not achieved. Attempt to increase device top maximum temperature by 5°C. If the device top maximum temperature is currently implemented, the rule is skipped.

002
The actual reflow time was less than the target reflow time minus 10 seconds (the system provides a 10 second success window). To compensate, the system will consider the actual cool down time. Next, the system will compute the necessary time extension to achieve the targeted reflow seconds. This time extension is implemented using a device joint average temperature maintain mode. The heating and flow sub-systems will be pulsed on/off to maintain the current device joint average temperature rather than simply turned off when the joint temperature is reached as in the original cycle.

003
The target device joint average temperature was not achieved. If the targeted device joint average temperature is at the minimum, the rule is skipped.
 
7.  
If the system changes any values, record the values on the BGA Rework Process Worksheets. Note: Access to BGA Process Worksheets requires a password.
 
8.  
After the additional Profile Cycles, the system will illuminate the "Done" light.

Note
If an optimized cycle can not be achieved, the system will report this condition to the user. Refer to Air-Vac manual for further information.

5.0 Profile Saving
 
1.  
Save the new Profile by clicking on the "Save" button in the upper left corner of the screen.
 
2.  
Enter the "Long Name" of the profile. (Example: ley 15 IC 907).
 
3.  
Click on the "Thumbs Up" icon, the OK, then Click on the "Thumbs Up" icon again.
 
4.  
Using "Print Options" print a copy of the graph page, and run a Data Point Summary Report.
 
5.  
Click on the "Thumbs Up" icon to display a new screen.
 
6.  
Check the "Build Profile" box.
 
7.  
Check the "Component Removal" box.
 
8.  
Check the "Removal Retry" box.
 
9.  
Check the "Component Placement" box.
 
10. 
Record the Nozzle Length: Click on the "Asterisk" (*) and select the nozzle size.
 
11. 
Record the Device Height: Click on the "Asterisk" (*) and select the BGA type.
 
12. 
Record the circuit board thickness: Enter the value.
 
13. 
Save the profile using the profile "Long Name" as follows:
1. Customer Name
2. Circuit Board Type
3. BGA Ball Count and Part Type
4. BGA Location
5. Nozzle Part Number
6. Operator Initials
14. 
Send the file to: Profile Library 1/99.
 
15. 
Click on the "Thumbs Up" icon.
 
16. 
Click on Save = OK.
 
17. 
If needed, the new Profile can be tested. It is suggested that the Removal cycle be performed using this new profile.
 
18. 
When complete, remove all Thermocouples except the #6 Bottom Side. Remove the circuit board from the machine, and store for further use.




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