Introduction: BGA Reworking Full Professional Procedure
In order to perform proper BGA reworking you need the right tools and equipment for the job. Proper procedure and setup is crucial in order to achieve longevity in the repair.
Kapton/ Aluminum Tape
Thermometer & Thermocouple
While there are several brands of BGA rework machines we selected an affordable station which is Made in USA. Other brands such as Scotle, LY, ACHI, Honton all can perform the same bga work it is up to the user to decide the best machine for them.
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Step 1: Preparation
By prepping the board for rework you can eliminate the chances of:
Proper preparation is removing moisture from the board, many boards have a MSL or moisture sensitivity level. The safest way to remove moisture without having the proper data sheet is to bake the board at 80c for 24 hrs.
Ultrasonic cleaning can also be used to remove any contamination. Special cleaning solution is used which can restore a board to factory new condition.
Step 2: Support
A key ingredient in successful bga reworking is making sure the board is properly supported. If this step is skipped there is the risk that the board will bow or flex. Sometimes it is very obvious and other times it is hard to tell. A flexed board may contain damaged internal traces or lifted pads. This damage is not repairable.
You want to ensure that the board is stiff in all areas, so that when the board is heated it will not bend or move in any direction. The area around the chip being reworked should have extra support as it will reach extremely high temperatures and it is crucial that the board remains flat or solder bridges will occur causing shorts.
Many BGA rework machines include basic support systems. There are 3rd party board supports that can sometimes perform better than stock supports.
Step 3: Profiling
Reworking is not as simple as heating the chip to 217c for the solder to melt. The board and chip need to be taken through a heating cycle. This heating cycle is called a profile which is basically a set of instructions that tell the heater how to heat the board, how long and how quickly. These set of instructions will ensure that the board and chip remain at safe heating levels and to eliminate thermal shock.
Profile development takes quite a bit of time and requires extra thermometers with thermocouples and a few test boards. All heating zones will need to be adjusted to work together so that the solder balls become liquidous and remain at a liquid state for a set period of time, this will ensure a solid and reliable joint throughout.
Step 4: Rework
After all the previous steps have been completed you can now confidently start the rework process. With the board properly prepped and supported you will use the appropriate tape to mask off areas that are not being directly reworked. Some components do not have a high tolerance to heat and must be covered. A thermocouple probe will need to be placed close to or underneath the chip being reworked. This will allow you to monitor the temperatures. Select the appropriate profile on the bga rework machine. Place flux on the sides of the chip using a syringe, the flux is extremely important and can make or break the reworking. After starting the process the profile will be activated. When the chip has been properly heated a cool down cycle will need to be initiated and is considered the final step.
Step 5: Conclusion
After the board reaches room temp you may remove it from the bga rework machine and supports. Remove all tape from the board and proceed to examine the solder balls. Proper inspection requires the use of an X ray machine or a Scope. Depending on the type of flux used an Ultrasonic bath may be needed to remove any harmful chemical residues left on the board. If using Kingbo this step is not necessary as it is a mildly active no clean flux. This means that is not corrosive and the residue is safe underneath the chip.