Ball Grid Array (BGA) Production
SMD ball grid array (BGA packages) enable high density connections to be made more easily to integrated circuits by allowing the under-side of a chip package to be used for the connectivity.
The Ball Grid Array (BGA) package was developed out of the need to have a more robust and convenient package for integrated circuits with large numbers of pins. With the levels of integration rising, some integrated circuits had in excess of 100 pins.
Surface Mount Technology
A Ball Grid Array or BGA Assembly is a form of surface mount technology (SMT) that uses tiny solder balls underneath the IC package to connect to the substrate or PCB. These gold balls convey electrical signals to the traces for the BGA.
BGA assemblies are being used increasingly for integrated circuits. They permanently mount devices and can provide more interconnection paths than in-line or packaging. Instead of just the perimeter, the entire bottom surface of the device can be used, which allows for a higher density of connections. The leads are also, on average, shorter than with a perimeter-only type IC, which leads to better performance at high speeds. The benefits of BGA are:
- Allows for efficient use of printed circuit board space
- Improves both thermal and electrical
- performance
- Lowers Inductance
- Controls Impedance
- Improves manufacturing yields when designed properly
- Reduces Package thickness allowing a space saving lower profile
- Improves re-workability resulting from larger pad sizes
- 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.
Originally published at Radio-electronics.com, written by Ian Poole
Ball Grid Array (BGA)
The conventional quad flat pack style packages had very thin and close spaced pins, and these were very easy to damage, even in a controlled environment. Additionally, they required very close control of the soldering process, otherwise the level of solder bridges and poor joints rose. From a design viewpoint, the pin density was such that taking the tracks away from the IC also proved to be problematic as there could be congestion in some areas. The BGA package was developed to overcome these problems and improve reliability from the soldered joints.
BGA Advantages
The Ball Grid Array was developed to provide a number of benefits to IC and equipment manufacturers as well as providing benefits to the eventual users of equipment. Some of the BGA
benefits over other technologies include:
- Efficient use of printed circuit board space, allowing connections to be made under the SMD package and not just around its periphery
- Improvements in both thermal and electrical performance. BGA packages can offer power and ground planes for low inductances and controlled impedance traces for signals as well as being able to route heat away via the pads, etc.
- Improvements in manufacturing yields as a result of the improved soldering. BGAs allow wide spacing between connections as well as a better level of solderability.
- Reduced package thickness which is a great advantage when many assemblies need to be made much thinner, e.g. mobile phones, etc.
- Improved re-workability resulting from larger pad sizes, etc.
These advantages have meant that despite initial skepticism about the package, it provides some useful improvements in many circumstances.
BGA Placement
he Ball Grid Array (BGA) 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 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.
In addition, the fact that the conductors are on the underside of the chip carrier means that the leads within the chip are shorter. Accordingly, unwanted lead inductance levels are lower, and in this way, Ball Grid Array devices are able to offer a higher level of performance than their QFP counterparts.
There are some potential problems with BGA that should be considered prior to finalizing your design.
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