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Emma / 2018-01-09
BGA is kind of package , called Ball Grid Array . uses a different approach to the connections to that used for more conventional surface mount connections. Other packages such as the quad flat pack, QFP, used the sides of the package for the connections. This meant that there was limited space for the pins which had to be spaced very closely and made much smaller to provide the required level of connectivity. The Ball Grid Array, BGA, uses the underside of the package, where there is a considerable area for the connections.
The pins are placed in a grid pattern (hence the name Ball Grid Array) on the under-surface of the chip carrier. Also rather than having pins to provide the connectivity, pads with balls of solder are used as the method of connection. On the printed circuit board, PCB, onto which the BGA device is to be fitted there is a matching set of copper pads to provide the required connectivity.
Apart from the improvement in connectivity, BGAs have other advantages. They offer a lower thermal resistance between the silicon chip itself than quad flat pack devices. This allows heat generated by the integrated circuit inside the package to be conducted out of the device onto the PCB faster and more effectively. In this way it is possible for BGA devices to generate more heat without the need for special cooling measures.
What are the BGA types ?
In order to meet the variety of requirements for different types of assembly and equipment, a number of BGA variants have been developed.
· MAPBGA - Moulded Array Process Ball Grid Array: This BGA package is aimed at low-performance to mid-performance devices that require packaging with low inductance, ease of surface mounting. It provides a low cost option with a small footprint and high level of reliability.
· PBGA - Plastic Ball Grid Array: This BGA package is intended for mid- to high-performance devices that require low inductance, ease of surface mounting, relatively low cost, while also retaining high levels of reliability. It has some additional copper layers in the substrate that enable increased power dissipation levels to be handled.
· TEPBGA - Thermally Enhanced Plastic Ball Grid Array: This package provides for much higher heat dissipation levels. It uses thick copper planes in the substrate to draw heat from the die to the customer board.
· TBGA - Tape Ball Grid Array: This BGA package is a mid- to high-end solution for applications needing high thermal performance without an external heatsink.
· PoP - Package on Package: This package may be used in applications where space is at a real premium. It allows for stacking a memory package on top of a base device.
· MicroBGA: As the name indicates this type of BGA package is smaller than the standard BGA package. There are three pitches that are prevalent in the industry: 0.65, 0.75 and 0.8mm.
When BGAs were first introduced, BGA assembly was one of the key concerns. With the pads not accessible in the normal manner would BGA assembly reach the standards that could be achieved by more traditional SMT packages. In fact, although soldering may have appeared to be a problem for a Ball Grid Array, BGA, device, it was found that standard reflow methods were very suitable for these devices and joint reliability was very good. Since then BGA assembly methods have improved, and it is generally found that BGA soldering is particularly reliable.
In the soldering process, the overall assembly is then heated. The solder balls have a very carefully controlled amount of solder, and when heated in the soldering process, the solder melts. Surface tension causes the molten solder to hold the package in the correct alignment with the circuit board, while the solder cools and solidifies. The composition of the solder alloy and the soldering temperature are carefully chosen so that the solder does not completely melt, but stays semi-liquid, allowing each ball to stay separate from its neighbours.
As many products now utilise BGA packages as standard, BGA assembly methods are now well established and can be accommodated by most manufacturers with ease. Accordingly there should be no concerns about using BGA devices in a design.
How to test BGA Assembly board ?
One of the problems with BGA devices is that it is not possible to view the soldered connections using optical methods. As a result there was some suspicion about the technology when it was first introduced and many manufacturers undertook tests to ensure that they were able to solder the devices satisfactorily. The main problem with soldering Ball Grid Array devices, is that sufficient heat must be applied to ensure that all the balls in the grid melt sufficiently for every joint to be satisfactorily made.
The joints cannot be tested fully by checking the electrical performance. It is possible that the joint may not be adequately made and that over time it will fail. The only satisfactory means of inspection is to use X-ray inspection as this means of inspection is able to look through the device at the soldered joint beneath.It is found that once the heat profile for the solder machine is set up correctly, the BGA devices solder very well and few problems are encountered, thereby making BGA assembly possible for most applications.
Also BGA could be repaired . Please notice .
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