9.2.2 BGA Component Rework Profile Development, Smart Track Method
| Printed Board Type: R | Skill Level: Expert | Conformance Level: High |
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Outline
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. |
|
Ball Grid Array Rework Station
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| 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 |
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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.
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.
- 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.
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.
- Test all Thermocouples prior to each use using a Digital
Thermometer.
- Test fit the the circuit board on the base of the BGA
rework machine. Consider the following:
- 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.
- Need to apply "heat shields" using Kapton tape
or aluminum foil.
- Location of placement of Thermocouples.
Figure 1: Place tip of
Thermocouple
#2 on center of
the BGA component. Secure with Thermal Adhesive.
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| 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).
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| 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).
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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.
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| 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.
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| |
| 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.
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| 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.
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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. |
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|
Figure 3: Place supports under
circuit board to support area around BGA Component to be
profiled.
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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.
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| |
| 2. |
If needed, remove tape previously placed on
the top of the BGA component to be profiled.
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| |
| 3. |
Plug in the Thermocouples as shown in Table
1 - Thermocouple Locations.
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| 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.
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| 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.
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| 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).
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| |
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Figure 4: Position the IR Sensor Thermocouple #1 approx.
2" from
edge of BGA component being
profiled.
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| 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).
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| |
| 8. |
Power on the machine. Pass "operator registration"
and "password log in" screens.
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| 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.
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| 10. |
Enter the following information onto the screen.
Values may vary depending on the application.
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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 |
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4.0
Profile Development Operation |
| |
| 1. |
Recheck the values are entered into the "Automatic
Temperature Profiling" screen.
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| |
| 2. |
In the Options section, Click the "Cycle Start/Stop"
icon to start the Automatic Temperature Profiling
cycle.
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| 3. |
If Automatic Temperature Profiling cycle fails
to start, follow the "Pop-Up" instructions.
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| 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.
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| 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.
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| 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.
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| 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.
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| 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.
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5.0
Profile Saving |
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| 1. |
Save the new Profile by clicking on the "Save"
button in the upper left corner of the screen.
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| 2. |
Enter the "Long Name" of the profile. (Example:
ley 15 IC 907).
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| 3. |
Click on the "Thumbs Up" icon, the OK, then
Click on the "Thumbs Up" icon again.
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| 4. |
Using "Print Options" print a copy of the graph
page, and run a Data Point Summary Report.
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| 5. |
Click on the "Thumbs Up" icon to display a new
screen.
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| 6. |
Check the "Build Profile" box.
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| 7. |
Check the "Component Removal" box.
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| 8. |
Check the "Removal Retry" box.
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| 9. |
Check the "Component Placement" box.
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| 10. |
Record the Nozzle Length: Click on the "Asterisk" (*) and select the nozzle size.
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| 11. |
Record the Device Height: Click on the "Asterisk" (*) and select the BGA type.
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| 12. |
Record the circuit board thickness: Enter the value.
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| 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.
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| 15. |
Click on the "Thumbs Up" icon.
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| 16. |
Click on Save = OK.
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| 17. |
If needed, the new Profile can be tested. It is suggested that the Removal cycle be performed using this new profile.
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| 18. |
When complete, remove all Thermocouples except the #6 Bottom Side. Remove the circuit board from the machine, and store for further use. | | |
