9.3.1 BGA Component Rework

Caution - Operator Safety: A thorough review of the equipment manual and comprehensive training is 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 before using this method. Plastic BGA components are susceptible to moisture absorption. Carefully evaluate pre-bake requirements.

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

• Layer delamination.
• Copper delamination, separation of pads, barrels of inner layers.,/li>
• Burns and solder mask chipping.
• Warp.

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

Receiving and Price Quoting

1. Upon receipt, the Shipper and Receiver log the customer-supplied materials and products into the Enterprise Resource Management System. Customer-supplied materials and product counts are verified.
2. The appropriate Sales Application Engineer reviews the project to confirm the project requirements, determine the solder chemistry classification, and verify if a solder stencil is in stock or needs to be ordered. Repeat projects will have a previously created process sheet in the Customer Process Specification database. A copy is printed and included with the job Traveler.
3. New projects require a thermal profile for the circuit board. See the process step listed below and procedure 9.2.1. We request a scrap circuit board assembly and extra components whenever possible for profile development.
4. Upon completion of the Sales Order, it is sent via email to the customer contact for confirmation of the process outlined and the charges listed. The schedule is confirmed, and the customer products and materials are transferred to the BGA rework area.

Project Process Development

1. Before starting the project, the Operator will review the following:
   A. Verify that circuit board and component part numbers and quantities match the Traveler.
   B. Visually inspect the circuit boards for temperature-sensitive components or parts. (Fiber optics, plastic connectors, batteries, etc.)
   C. Ensure the BGA machine maintenance is current and the appropriate checks are done before operating the BGA machines.
2. All Circuit boards are baked for a minimum of 12 hours at 125 °C unless otherwise instructed by the customer. In addition, all BGA components that are received in unsealed packaging are baked per the Moisture Sensitive Device Control Procedure unless otherwise instructed by the customer.
3. Thermal Profile development is required for all projects. If available, the Operator will develop the thermal profile using a customer-supplied scrap assembly that is the same as the circuit boards to be processed. If the customer cannot supply a scrap board, the thermal profile is developed during the initial removal process. In both cases, the operator will identify the following board conditions and start with the most logical machine setting:
   A. Solder chemistry, leaded or lead-free.
   B. Board thickness.
   C. Board and component density and layout.
   D. Component ball count and design.
   E. Under-fill or conformal coating surrounding the site.
   The thermal profile is created by placing thermocouples at various locations to monitor and adjust the heating source time and temperature from the bottom side heat plate and the top side nozzle. Multiple machine cycles may be required to achieve the desired results. Upon completion, the profile is stored in the machine and saved in the Customer Process Specification database for current and future applications. See procedure 9.2.1 for more detailed information.
4. Additional notes are added to the Customer Process Specification to identify special handling or other steps needed to achieve an acceptable condition. These include adjacent components that need removal, specific masking or shielding requirements, and other conditions that may impact the process.

BGA Rework Process

1. Operators initially review the Traveler and additional paperwork to ensure the instructions are clear and match the circuit boards to be processed. Any questions are directed to the Sales Application Engineer or the customer for clarification.
2. If circuit board disassembly is needed, all materials must be labeled and noted on the Traveler.
3. The operator will locate and load the removal profile specified on or with the Traveler for the component removal. The removal process is visually monitored through a microscope. When the BGA component solder balls reach a molten state, the vacuum pick-up of the component is initiated.
4. Site cleaning is done using a non-contact site cleaning tool or solder wick. If underfill or conformal coating is present at the site, additional steps are required to remove it. Typically, heat, machining, or chemical stripping of the site is needed. Refer to the Sales Application Engineer, customer instruction, or the product data sheet for the appropriate process.
5. No-clean solder paste or flux is utilized for BGA assembly and rework unless otherwise instructed by the customer.
6. After the site cleaning process, the circuit board is inspected to ensure the mask is undisturbed and the site is suitable for installation. If solder mask touch-ups or other issues are identified, they are reviewed with the Sales Application Engineer for direction.
7. Solder stencils deposit the solder paste onto the site. Care is taken to ensure the paste is deposited evenly and completely.
8. The installation of the BGA component is completed following the programmed profile specified on or with the Traveler. The installation process is visually monitored through a microscope. When the BGA component solder balls and solder paste reach a molten state and ball collapse is confirmed, the placement process is complete.
   Note: High-temperature solder balls will not collapse and will rely on the paste wetting to the ball.
9. Upon completion of the placement process, the circuit board is visually inspected at the BGA placement site and all adjacent areas. Touch-up of the circuit board is completed if needed.
10. X-ray inspection is completed at the BGA placement site and adjacent areas. See procedure 9.1.2 for additional information. Any potential workmanship or unacceptable conditions are reviewed with the Sales Application Engineer for direction.
11. Re-assembly of any removed components or hardware is performed.
12. QC Inspection completes final inspection.