How can we identify the BGA area of PCB

BGA area of PCB
BGA refers to ball grid array package and is the best choice for high pin count packages. The pins of the chip using the  are distributed on the bottom of the chip in an array arrangement, which is represented by a small ball. In order to correspond to the ball shape of the BGA package chip pins, the PCB pads are also arranged in a ball-shaped array distribution, so the BGA area of the PCB can be identified by the shape on the pad. At present, due to its advantages of reducing chip size and good heat dissipation, a large part of BGA-packaged devices have been widely used in high-end consumer markets such as mobile phones, digital cameras, network and communication equipment, and various flat-panel displays.
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The BGA package generally has many pins, so its pin position determination is more complicated. And for maintenance personnel, foot identification is a more important content. Because if you don’t know how to identify the pins, you can’t detect the fault point. In the BGA pad area on the PCB, there will be a mark to identify the pin, take the triangle mark in the upper left corner of the array as an example. Taking the sign as the starting point, the clockwise row is arranged in order by 1, 2, 3…, and the counterclockwise row is arranged in order by the letters A, B, C… It is worth noting that the alphabetical arrangement should exclude the letters I, O, Q, S, X, and Z, that is, the alphabetic order remains unchanged and these letters are eliminated. The main reason for not using these letters is to avoid confusing letters with numbers like 1, 0, etc. If the letters have not been arranged until the letter Y, then the letters can be sequentially extended to AA, AB, AC… According to the above arrangement, the pin number of the corresponding pin can be found, that is, the 1st pin or the A1 pin. If it is a BGA chip, also find its mark point, which corresponds to the pins on the pad one by one. Taking the flag bit on the chip as the starting point, according to the arrangement on the pad, it can be known that the clockwise row is alphabetical, and the counterclockwise row is digital.
How to install BGA components
There will be some differences in the installation of BGA components and other SMT components. To mount a BGA device, first apply solder paste to the PCB, and then place the BGA device correctly by a SMT machine or by hand. It is a feature of BGA components that they can automatically calibrate as the solder liquefies and hardens. The element is then heated and the device pins can be connected to the PCB. If you are soldering by hand, you can use the mounts to hold the components in place. If the PCBA is going through a reflow oven, the oven settings can be adjusted appropriately to ensure a good solder connection.

in conclusion
For the installed BGA components, because the pins are distributed in a spherical array on the bottom surface of the chip, the pins cannot be seen after installation, so it is more difficult to test. To solve this problem, we use X-ray equipment to check for welding defects. Generally speaking, the more common solder defects are solder bridges, solder seam defects, solder ball damage and solder ball oxidation. X-rays also have their drawbacks, as most work is done from top to bottom and can only show the outline of the solder, not if the cross-section solder is defective. Defects are better found using cross-sectional X-rays, but this method is extremely expensive. So it’s important to get things right the first time at the very beginning of installation, proper placement of solder paste and BGA components, and proper reflow oven settings. Not only does this save a lot of time, it also avoids having to redo the BGA chip.