Let's talk about the rework of BGA

Talking about the rework of BGA

BGA's basic cognition and unique strengths

BGA, or Ball Grid Array Packaging Technology, is designed to strategically arrange circular or columnar solder joints in the form of an array at the bottom of the chip. Compared with traditional chip packaging methods, the most significant difference of BGA packaging is that the solder joints are completely hidden under the chip, which brings many irreplaceable advantages to it.

The first is a higher density pin layout. Since the solder joints are arranged in an array at the bottom of the chip, it can get rid of the space limitation of traditional packaging pins arranged around the chip and can accommodate more pins on the same chip area, which is crucial for modern electronic products that pursue miniaturization and high performance, and can effectively improve the connection efficiency between the chip and external circuits.

The second is better electric heating performance. The array of solder joints makes the conduction of current and heat more uniform, reduces interference and delay during signal transmission, and is also conducive to the rapid dissipation of heat generated during chip operation, ensuring the stability and reliability of the chip during high-load operation.

However, this unique structure also makes the BGA rework process relatively complex, with high requirements for operating technology and equipment, which is also one of the characteristics that BGA packaging needs to focus on.

Common BGA types and their characteristics

2.1 PBGA (Plastic Package)

PBGA is widely used in the market, and its most prominent advantages are its low cost and relatively easy machining process, making it suitable for large-scale production.

In terms of characteristics, the melting point of conventional solder used in PBGA varies depending on the type: lead-based solder has a melting point of 183°C and lead-free solder has a melting point of 217°C. This difference in melting point requires special attention during the rework process to ensure precise control of the welding temperature.

In addition, PBGA has an important consideration - it must be treated well against moisture. Because plastic packaging materials are easy to absorb moisture from the air, if the moisture is not properly protected, moisture evaporation may cause the package to crack as the temperature rises during soldering or rework, affecting the performance and life of the chip.

2.2 CBGA

CBGA is known for its excellent moisture resistance and stable construction, which can maintain good working conditions in harsh environments.

Its characteristics are as follows: the use of a solder ball with a high melting point, the solder ball composition contains 90% lead and 10% tin, which allows the solder ball to maintain stable morphology and performance even in high-temperature environments. The diameter of the welding ball is 0.889mm, which helps improve the precision and reliability of welding.

At the same time, CBGA does not produce solder residue during the soldering process, which reduces a lot of trouble for subsequent inspection and rework work, and also reduces the risk of problems such as short circuits due to solder residue.

BGA rework process analysis

3.1 Pretreatment preparation: the key link that determines the success or failure of rework

The quality of work in the pretreatment preparation stage is directly related to the success rate and efficiency of the entire rework operation, so it must be given due attention.

Drying treatment: remove moisture to ensure safety

Drying treatment is a key link in the preparation of pretreatment, and its core purpose is to completely remove residual moisture from the chip and circuit board, avoiding component damage or soldering failure caused by moisture evaporation during the subsequent heating process.

In terms of operating specifications, two points must be strictly observed: first, after baking, the subsequent rework process must be completed within 24 hours to prevent the components from absorbing moisture from the air again; Second, before drying, temperature-sensitive components on the board, such as batteries and optical fibers, need to be removed in advance, which are likely to lose their original functions if exposed to high temperatures.

Protective measures: meticulous protection to avoid damage

To prevent damage to peripheral components caused by high temperatures and operations during rework, components within 10mm of the rework area need to be effectively protected.

The specific protection method is to use 5-6 layers of high-temperature tape to seal and cover the relevant areas, focusing on protecting radiators, capacitors and other components that are susceptible to high temperatures or are more fragile, ensuring that these components are not damaged by excessive temperature or accidental touch during the repair process.

Tool configuration: reasonable selection, stable support

In terms of tool configuration, the selection of heating nozzles needs to be determined according to the specifications of the BGA, usually using nozzles with BGA size plus 2-5mm to ensure uniformity and targeting of heating.

For large PCB boards, due to their large area, they are prone to deformation due to uneven heating during rework, so they need to be supported. When supporting, the center of the board should be preferred as the support point, and be careful not to rely on the components on the board for support to avoid damage to the components.

3.2 Temperature curve setting: precise control to ensure quality

Since many factors such as board material, component size, and solder type affect temperature during BGA rework, every rework operation requires precise setting of the temperature profile.

When setting temperature profiles, historical curve data from this model BGA or similar board should be prioritized, as these data have been proven to provide a reliable reference for temperature settings. If historical data is not available, field testing is required, using a test plate of the same specification as the rework board, and the thermocouple drilling is fixed to the weld ball to accurately monitor temperature changes during the welding process.

In terms of the selection of curve type, it is recommended to use a triangular tent curve. The heating rate of this curve should be controlled at <3°C/sec and the cooling rate should be controlled at <5°C/sec, so as to avoid damage to components or circuit boards caused by thermal shock caused by rapid temperature changes.

In addition, temperature control focuses on preheating the bottom of the PCB, which effectively prevents the board from deforming due to excessive local temperature. At the same time, the entire heating process must be controlled in strict accordance with the melting point temperature of the solder used to ensure that the solder can fully melt and form a good solder joint without damaging the components due to excessive temperature.

Through the above detailed explanation of BGA's basic cognition, type characteristics and rework process, it is hoped to provide a practical reference for relevant practitioners. If you would like to delve deeper into a particular aspect or have other specific requirements, please feel free to ask.