BGA (Ball Grid Array) is a technology for surface mounting ICs using small balls on the underside of the chip package instead of pins. BGA is sometimes referred to as CSP (Chip Size Package). The term BGA is most commonly used when talking about packages that are 4, 6, or 8 balls in diameter.
The distinguishing features of a BGA are:
Very small package size (about 1/20th the area of a comparable pin-based package).
All contacts are on the bottom surface of the chip.
Each contact is made with a solder ball, not a wire.
Solder balls usually have to be reflowed in order to make reliable connections to the substrate. The solder balls are melted with a hot gas at temperatures over 400° C (750° F). BGA packages typically use larger balls than CSP packages. The larger balls allow for better distribution of the gas at the bottom of the package.
The balls do not have to be round as in CSP packages; they can be made out of any shape and are frequently rectangular or triangular for more reliable mounting to a PCB.
BGA packages are mechanically very robust. The balls are usually attached to the chip with a small amount of adhesive, and not with solder. This allows for some misalignment between the balls and contact pads on the chip without causing mechanical damage. If there is excessive misalignment, it will result in poor electrical contact and possibly solder fatigue.
BGA packages are generally not as reliable as CSP packages (more time consuming and costly to repair). They often have larger pads to accommodate the increased thermal expansion. The small size of the package makes it hard to maintain a good temperature distribution during soldering and to perform reliable visual inspection after assembly.
BGA is not a technology, but rather a device classification. There are many variations of BGAs, such as multi-chip BGAs and flip-chip BGAs.
Are there disadvatages?
BGA packages have some disadvantages compared to pin-based packages:
Each contact point, or ball, must be soldered to the PCB. This requires a reflow process at temperatures above 400 °C. At this temperature, the solder can damage the substrate material. Because of this, BGAs are not used in applications where small size is not essential and a larger package can be used. BGA packages are not suitable for applications where reliability is essential and small size is not an issue.
A high level of heat is required to solder the balls to the substrate, and this can damage the chip. The balls are usually attached to the chip with a small amount of adhesive, and are not soldered in place as with CSPs. Poor thermal contact between the ball and substrate may result in large temperature differentials across the ball, causing solder fatigue and resulting in unreliable operation or even damage to the IC. The BGA must be attached flat on its side to a heat sink or a PCB.
The substrate might not be able to withstand the temperature generated by the soldering process. In this case, the chip must be attached to a heat sink with a good thermal conductivity material in order to dissipate the heat. This is not always possible, for example if the chip must be used in an area where there is no room for a heat sink.
The balls can easily fall off if excessive force is applied to the package during handling. The balls are permanently attached to the substrate with an adhesive. This is usually good for reliability, but if a ball comes off, it will be hard to find it.
What are some solutions to the problems of using BGA?
BGA packages can be used in many applications where the benefits outweigh the disadvantages. A few solutions are:
The entire PCB can be coated with solder, and then rework is done using a solder bath or hot air. This allows the use of BGA chips in applications where they would otherwise not be feasible.
BGA packages can be used in low-reliability applications, but only if the surface mounting technology is handled by a skilled operator who is able to do visual inspection after assembly. The operator must be able to recognize if a ball came off the package, which is not always easy because the balls are usually very small.
BGA devices are often used in high-reliability applications where yield is not an issue and the device can be replaced easily in case of failure.
Understanding the importance of BGA Sockets for BGA chips
BGA sockets are used for surface-mounting BGAs onto PCBs. BGA sockets help to mount the BGA chips onto PCBs without much hassle. The main problem of mounting an IC onto a PCB is that it can be very difficult to locate the pins of the IC on a PCB and solder them individually. Also, the mounting process can be very time consuming and frustrating if not done correctly. By using BGA sockets, these problems are solved. A BGA socket is made of plastic in the shape of a rectangle and has spaces on its underside to accommodate each solder ball of the BGA chip.
BGA sockets come in two types: active and passive. An active BGA socket has electrical contacts on its underside to which the solder balls of the BGA chip are connected. A passive BGA socket does not have any contact pads on its underside. Instead, it is connected to a PCB using through-holes or surface mount technology (SMT) components. In this article, we will only be looking at active BGA sockets.
BGA sockets are available in a variety of sizes depending on the size of the BGA chip that they are designed to accommodate. Some BGA sockets are designed to accommodate only one BGA chip, while others accommodate two or even four chips. The size of a BGA socket is usually specified in terms of the number of rows and columns on its underside. For example, if a BGA socket is designed to accommodate a 4×4-ball BGA chip, then it would have 16 contact pads arranged in 4 rows and 4 columns.
BGA chips are available in a variety of sizes. The number of balls on the underside of a BGA chip is usually specified as x4, x6 or x8. A x4-ball BGA chip has 4 balls on its underside. A x6-ball BGA chip has 6 balls, and so on.
BGA chips are available in several different ball sizes. The size of the balls is usually specified as x1, x2, x3, etc. A ball size x1 is the smallest ball size and it has a diameter of 0.4 mm. A ball size x4 is the largest ball size and its balls have a diameter of 1.0 mm. The larger the ball size, the larger the footprint of the BGA chip on the PCB.
Why should manufacturing companies consider BGAs instead of CSP packages:
There are several reasons why a manufacturing company should consider using BGAs instead of CSP packages:
The BGA package can be smaller than its CSP counterpart.
BGAs are capable of greater packing density than any other surface-mount package.
BGA packages are often cheaper to manufacture due to the smaller size, fewer balls, and fewer added features. In addition, BGAs can be made with lead-free solder. The solder balls can be placed on the BGA chip with robotic equipment, which is much more efficient than hand placement of CSP packages.
BGA packages have a greater variety of shapes compared to CSP packages. This allows for packaging that takes advantage of various mounting geometries and reduces the height of the PCB.
The small size of BGAs makes them more suitable for applications where space is limited, such as mobile phones.
BGA packages are less sensitive to misalignment than CSP packages because they use a small amount of adhesive to secure the balls to the chip. This allows for a larger margin of error during mounting.
BGA packages can be used to make a better use of space in high-density applications. For example, stacked BGAs formed by placing one BGA on top of another are commonly used in handheld devices.
Today, BGA chips are used in many different applications from high power radio frequency amplifiers to lowest power sensors. BGA offers the smallest packages available, which are small enough to accommodate a large number of pins on the chip. Additionally, BGAs offer large thermal dissipation capability yet still maintain high reliability due to the small size/mass of the package.
With BGA, you will never have to worry about a connector or a lead breaking off of your device. BGA chips are mechanically very rugged and difficult to damage. BGA does not require a socket, which means there is no need for a secondary carrier board. This makes it very cost effective.
As you can see, BGA is a very interesting technology that gives the utmost flexibility in the design of chip packages, but at the same time it requires a lot more effort and expertise than other surface mount designs. When considering BGA for your product, there are many things to be considered – size, cost, reliability, complexity of design, but most importantly your specific application.