IC Substrate - What is a BGA?

What is a BGA?The full name of BGA is “Ball Grid Array” (Ball Grid Array), meaning a printed circuit board with a ball grid array structure. PCB boards with BGA generally have more small holes, through-holes are usually designed as finished holes with a diameter of 8-12mil, through-holes need to be plugged, pads are not allowed to be inked, and pads are not allowed to be drilled.

General rules for BGA pad design

1) The pad diameter is usually smaller than the solder ball diameter. In order to obtain reliable adhesion, it is usually reduced by 20% -25%. The larger the pad, the smaller the wiring space between the two pads.

2) The diameter of the pads on the substrate side of such boards is the same as the diameter of the pads on the PCB. The pads should be designed so that the amount of solder paste leakage due to stencil openings is ≥ 0.08mm3 , which is the minimum requirement to ensure solder joint reliability.

The main process flow of BGA packaging includes solder ball production, substrate production, chip bonding, packaging solidification, and slitting packaging.

1) Solder ball production: Using high-purity tin-lead alloy or lead-free materials to produce solder balls, forming a regular spherical pin array.

2) Substrate production: Using multi-layer printed circuit boards as substrates to achieve high-density and high-performance electrical interconnection.

3) Chip bonding: Attach the chip to the substrate and connect it to the substrate using lead-free or lead-based solder.

4) Packaging and curing: The chip is encapsulated with epoxy resin to protect it from environmental influences.

5) Split packaging: Cut the packaged chip into separate BGA packages.

Process flow of BGA package

1.Disc thinning

Wafer thinning is the first step of BGA packaging,which is mainly realized by grinding wheels rotating at high speed on the backside of the wafer. During this process, water cooling and cleaning operations are required to prevent high temperature buildup and debris collection.If thinning to a certain thickness is required,polishing is also performed to eliminate internal stress and reduce the risk of chip surface cracking.

2.Wafer Dicing

After the wafer thinning is completed, the wafer is fixed to a metal ring and cut to make it an individual chip. The main cutting methods are blade cutting and laser cutting. Laser cutting is gradually becoming a more viable option due to its lack of external force, small cutting width and high quality.

3.Chip Mounting

Chip mounting is to fix the chip on the substrate, usually using materials such as silver glue or DAF film. The purpose of this step is to fix the chip and effectively conduct its heat to ensure the normal operation of electronic components.

4.Plasma Cleaning

Plasma cleaning is an important step before the welding line, it uses ionized argon ions, electrons and other active particles to make the pollutants into volatile gases and remove. This process effectively improves the cleanliness of the substrate and chip before soldering, thus enhancing bonding during the soldering process.

5.Lead wire soldering

Lead bonding is the core of the packaging process, whereby the lead wires are connected to the aluminum pads on the chip and the metal pads on the substrate to achieve electrical conduction. This process requires a high degree of accuracy and reliability.

6.Molding

The sealing step protects the chip from the environment by injecting a sealer that melts at high temperatures into the mold cavity and then cures. Typically, the epoxy resin is cured with additives to ensure chip stability.

7.Post-curing

After sealing, the encapsulant usually needs to be cured at high temperature to fully react and stabilize its molecular structure. This process improves the hardness of the molded body and eliminates internal stresses, thus ensuring the durability and reliability of the product.

8.Marking and Cutting Sorting

The final stage consists of marking Prints on the front of the chip to facilitate product tracking and identification, followed by cutting or stamping the entire BGA substrate into individual chips to complete the packaging process.

Significant Advantages of BGA Packaging Technology

The technology stands out with its unique pin layout design, which realizes high-density integration in a compact space and offers the possibility of building more complex and fine circuit networks.This layout strategy not only optimizes space utilization,but also promotes the development of electronic equipment in the direction of miniaturization and high integration. From the perspective of heat dissipation performance,the solder balls in the BGA package structure are directly connected to the printed circuit board (PCB), which builds a highly efficient heat conduction path,effectively enhancing the system's heat dissipation efficiency,and ensuring the stability and reliability of the components under prolonged high-load operation. Furthermore, the introduction of automated production lines,especially the application of high speed surface mount equipment,has greatly improved the production efficiency of packaging and reduced labor costs, while also ensuring the stability and consistency of product quality.

Although BGA packaging brings many advantages, but its practical application also faces some challenges that can not be ignored. The primary problem lies in the high standard of solder joint reliability.As the solder joint carries the dual functions of electrical connection and mechanical support,its quality is directly related to the stability and reliability of the entire package structure.The appearance of any empty welding, false welding and other problems may have a serious impact on the circuit performance, or even lead to the failure of the entire package. In addition,the complex structure of the BGA package also brings difficulty to its rework work. Once repair or replacement is required, the complexity of the soldering and disassembly process often increases the operational difficulty and cost. Finally, for some specific application scenarios, such as high hermeticity requirements or devices that need to withstand extreme environmental conditions, it may be less than ideal due to its sensitivity to moisture, which to a certain extent limits the scope of its application.

BGA packaging is a surface mount technology characterized by the formation of a regular spherical pin array at the bottom of the package. This packaging method has advantages such as large pin spacing, good thermal performance, and superior signal transmission performance, making it widely used in high-speed and high-performance integrated circuits.