BGA Assembly
BGA is also called ball pin grid array packaging technology, which is a high-density surface mount packaging technology. At the bottom of the package, the pins are spherical and arranged in a grid-like shape, so it is called BGA.

Features of BGA

 Reducing the package area
The BGA layout can reduce the packaging area and greatly improve the space utilization rate. We can install more components and manufacture lighter devices.

 Increasing functions number of pins
As the BGA layout increases the space utilization rate, the product functions increase accordingly. And one of the advantages of BGA is that the number of I/O pins has increased, and the pin spacing has not decreased but increased, thereby increasing the assembly yield.

 Good electrical heating performance and improved reliability
Although the power consumption of the product can be increased, the BGA can be welded by the controllable collapse chip method, which can improve its electric heating performance. And the assembly can be coplanar welding, which has high reliability.

 Reducing costs
Most BGA designs are small in size, smaller size and convenient manufacturing routes can ensure that we reduce manufacturing costs. Therefore, this process is very suitable for mass production.

The Types Of BGA 

(1) PBGA (Plastic Ball Grid Array)
The PBGA package consists of chips mounted and interconnected to a double-sided or multi-layer PCB substrate. Through holes interconnect the signal printed lines on the top surface to the corresponding pads on the bottom of the substrate. After die bonding and wire bonding, the assembled part is molded and encapsulated by a transfer molding or injection molding process. PBGA is currently the most widely used BGA device. Mainly used in communication products and consumer products. Because PBGA has good electrical properties, high interconnection density, and good thermal comprehensive performance, it is widely used in SMT assembly.

(2) CBGA( Ceramic Ball Grid Array)
CBGA uses multilayer ceramics as the base material. Its advantages include: (1) Packaged components have high reliability and excellent performance. (2) Good coplanarity and easy welding. (3) Insensitive to moisture, long storage time. (4) Good electrical performance. (5) High packaging density

(3) TBGA (Tape Ball Grid Array)
TBGA is a package form that uses copper/polyimide carrier tape as a substrate to connect the chip to the solder ball and the PCB. TBGA has the following characteristics: (1) Good thermal matching with epoxy resin circuit board (2) It can be aligned with the PCB pad through the edge of the package body (3) Sensitive to humidity and heat

BGA process flow

In the BGA assembly process, every step and every process parameter will affect the BGA assembly. Therefore, every step of BGA assembly must be strictly controlled. For the electronic assembly process of tin-lead and lead-free electronics, there is not much difference between the solder paste printing and the placement process. The main difference lies in the setting of the temperature profile during the reflow process. There is a big difference between the tin-lead reflow soldering process and the lead-free reflow soldering process. In addition, due to the different BGA package forms, the thermal resistance is different. In order to meet the requirements of the reflow soldering curve, there are also certain differences in temperature settings and time.
Solder paste printing
The storage conditions of solder paste are generally 3-6 months at 2-5°. The solder paste needs to be warmed naturally before printing, and the warming time is 4-8 hours. Before the solder paste is warmed to room temperature, do not disassemble the container or stir the solder paste and force it to reheat, so as not to cause the flux to be analyzed. The amount of solder paste printing should be appropriate, and the printing template generally uses stainless steel.
When printing solder paste, 60 is generally used. The strength of the stainless steel scraper is controlled at 35-100N. The printing speed is generally controlled at 10--25miifs. The demolding speed after printing is generally set at 0.5-1.0 miifs. During printing, the temperature should be controlled at about 25°, and the humidity should be controlled at about RH55%.

The main purpose of the patch is to align each solder ball on the BGA with the pad on the PCB. Because the BGA solder balls are located at the bottom of the package, special equipment must be used to align them. The placement accuracy of the placement machine with BGA must reach about 0.001 min.
Reflow soldering
Reflow soldering is a difficult process in the BGA assembly process. Setting process parameters and obtaining a suitable temperature profile are very important for good BGA soldering. Due to the different packaging forms of BGA, the thermal resistance of CBGA is greater than that of PBGA. In order to achieve the same temperature, CBGA requires a higher temperature setting and longer preheating time than PBGA. For tin-lead solder paste and lead-free solder paste, the temperature setting and heating time are significantly different.
Warm-up stage:
The main purpose of preheating is to heat the PCB and its components uniformly, and at the same time have a baking effect on the PCB and components. The heating rate of the preheating stage is generally controlled at 3℃/s, and the preheating time is between 60-90S.

Activation stage:

The main purpose of the activation stage is to activate the flux in the solder paste to remove the oxides on the surface of the pad and the surface of the solder paste alloy to achieve a clean metal surface and prepare for the solder paste reflow. For tin-lead soldering, the temperature at this stage should be maintained at 60-120 S at 150-180°C. For lead-free soldering, the soldering at this stage should be maintained at 160-200°C for 60-180 S.


Reflow stage:
The main purpose of the reflow stage is to wet the solder pads and the pins of the components to achieve good soldering requirements. For lead-free electronic assembly, there is a cloud of Sn alloying alloy in lead-free solder, which is more likely to form thicker metal compounds at high temperatures and cause solder joint failure. For SnPb soldering, it is generally required to control the time above the melting point of 183°C to 60-90S. For lead-free soldering, it is generally required to control the time above the melting point of 217-219°C within 60-120 S.
Cooling phase:
The main purpose of the cooling stage is to refine the crystal grains while the solder joints are solidified, inhibit the growth of intermetallic compounds, and improve the strength of the solder joints. Generally, the cooling rate is controlled at 1-3°C/S.






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