Does your integrated circuit have lots of pins? Maybe even more than 100 pins? If that is the case, you should look for a convenient and robust package for your integrated circuits. However, guess what, you don't need to research around, we know what you should do!
QFP packages were more prone to damage, even under controlled conditions, as they had very closely packed and thin pins. Further, if its welding was not properly supervised it would result in bad connections. You might also encounter high pin density in some areas leading to congestion.
However, rest assured, Ball Grid Array SMT package is what you should look for. It is the solution to these problems, and your soldered joints’ reliability will improve big time. In this guide, we will mention all the different details that you need to know about BGA SMT packages.
1、PCBs with BGA
A ball grid array is a chip carrier – surface mount technology – used in integrated circuits. If you want to mount your microprocessor permanently, then you should use ball grid arrays (BGA).BGA will supply you with more interconnections pins when compared with what you get from the flat package.
The complete bottom area of your device will be utilized rather than just the perimeter. Further, the leads are also smaller in size, providing you with more performance at high speeds. Traditional pin grid array (PGA) packages have led to the development of BGA packages. PGA is a package which has pins arranged in a grid pattern on its one face, covering it covering it fully or partially. While operating, the pins send electrical signals between the printed circuit board (PCB) and integrated circuit (IC).
Now let’s get to how BGA is different from PGA. In BGA, you will need to replace the pins by pads on the package’s bottom surface. In the beginning, you will do it by sticking small solder balls. You can place these solder spheres either manually or by using automatic devices. Figure 1 shows a close up of ball grid array IC.
Generally, copper pads link together the BGA IC and a printed circuit board (PCB). The pattern of these pads complements the solder balls. In more innovated technologies, the solder balls can be placed both on the BGA package and the PCB. If you are planning on developing multi-chip modules, you can use solder balls to join together different packages. Figure 2 illustrates the footprint of BGA IC on a printed circuit board.
With PCB BGA, you will get the following advantages:
1. BGA package eliminates the issue of developing small packages for ICs with lots of pins. Traditionally, dual-in-line and pin grid arrays surface mount packages had very little space between the pins. They provided a huge disadvantage for the soldering process with more pins. However, you will not need to worry about accidentally soldering together two pins with BGA packages.
2. Again, when compared with packages with legs, The BGA package has a lower thermal resistance when placed on the PCB. That permits the heat that is produced by IC in the package to conduct through the PCB easily. Can you guess how that is a good thing? Of course, it will save your chip from overheating.
3. Do you know which property causes unwanted signals distortion in high-speed electronic circuits? The unwanted inductance in an electrical conductor is responsible for this phenomenon. However, BGAs have very little distance between PCB and the package which in turn leads to lower lead inductance. Thus, you will get top-class electrical performance with pinned devices.
4. With BGAs, you can effectively utilize your printed circuit board space. You will be able to make connections right below the surface mount device (SMD). The connections are no more limited to just SMD package periphery.
5. Another advantage that will come with BGA is the reduced thickness of the package. That sounds great. You can easily fabricate the PCBs in small electronic devices, such as smartphones.
6. Last but not least, you will get enhanced re-workability because of bigger pad sizes.
2、BGA Welding Basics
It is very crucial to carefully choose the soldering temperature and composition of the solder alloy. It would help if you made sure that the solder of your BGA PCB package doesn't completely melt. It needs to stay half-liquid, permitting every ball to lie separately from other balls.
Luckily, BGA welding kits or welding machines are widely available in the market. You can also buy them online. Usually, the welding machines come with the following main features:
- Rework BGA and other SMDs.
- Solder, De-solder, Mount, and Remove your BGA package manually.
- Integrated with infrared heating plate and hot air heaters.
- Easy to use. It will have a touchscreen interface.
- Used to accurately control temperature
- and emergency protection.
Figure 3 demonstrates a BGA welding or rework station.
In the next chapter, we will explain in detail the BGA welding process.
3、BGA Welding Process
Initially, one of the major problems about BGA was whether it would be able to offer reliable welding procedure. You don’t need to get confused with the term welding; it is just another word for soldering. Moreover, as BGA has pads rather than pins on the bottom surface of the device, it is crucial to make sure that the correct welding procedure is adopted.
Luckily, BGA welding methods have shown to be more reliable than traditional quad flat packs. All you need to make sure is that the method is set up correctly. That, in turn, means that BGA assembly will also be more dependable. Thus, BGAs have been greatly used in both prototype PCB assembly and mass production PCB assembly.
Carefully choose the size of the solder balls while performing BGA welding. You will need to put a very carefully measured quantity of solder. Further, the solder will melt when the solder balls are heated. Once melted, surface tension will allow the molten solder to align the package with the PCB correctly. The solder will then cool and solidify. Thus, your BGA PCB will be all ready. Figure 4 shows the hands of an expert attempting to repair the solder balls of BGA.
In the beginning, PCB BGA assembly was one of the major fears. Engineers were not sure whether PCB BGA assembly would be able to achieve the reliability level of traditional SMT methods. However, BGAs have proved themselves to be more reliable. Therefore, BGAs have been greatly used in both prototype PCB assembly and mass production PCB assembly.
You will need to use reflow methods to solder a BGA package. You may be wondering that why that is. The main reason behind this is that you need to make sure that solder melts beneath the BGA modules themselves. For this purpose, the whole assembly requires to reach up to the melting temperature. Finally, only reflow methods can achieve this purpose.
Now, many devices are utilizing the BGA packages as the standard PCB BGA packages. Therefore, the PCB BGA packages assembly techniques are more reputable now. Manufacturers can handle them quite comfortable. In the same way, BGA devices should not lead to any fears when being used in a design.
As we have already described in the first chapter, the BGA package does not use the sides of IC for the connections. It uses the bottom surface of the integrated circuit and thus provides more space for the connections. Further, BGA uses copper pads for connections rather than the pins.
The copper pads have solder balls which have a complement set of copper pads on a PCB. Thus, they can be easily fitted on the PCB. It is interesting to note here that the pads are arranged in a grid pattern under the IC. Therefore, it is this specific arrangement that gives Ball Grid Array their name.
Generally, the PCB BGA packages have a pitch size of minimum 0.3mm. Moreover, the length between two BGA packages is usually around 0.2 mm. Moreover, the least distance to the circuit line is around 0.2 mm. These are the general sizes; if you are looking for different sizes, you may contact the manufacturers. Figure 5 is showing a small BGA package on a finger. You can guess its size.
There are six different kinds of BGA package. We will go through each of them in this section.
1. Moulded Array Process Ball Grid Array (MAPBGA): It is a BGA package which provides low inductance and simple surface mounting. You can use it for low-performance to medium-performance devices. It is highly reliable, cheap and has a small footprint.
2. Plastic Ball Grid Array (PBGA): Again, this BGA package provides low inductance, simple surface mounting, high reliability and is cheap. Further, its substrate has more copper layers which allow handling of more heat dissipation levels. You can use it for medium-performance to high-performance devices.
3. Thermally Enhanced Plastic Ball Grid Array (TEPBGA): Just like its name sound, this BGA package can handle great levels of heat dissipation. Its substrate has solid copper planes.
4. Tape Ball Grid Array (TBGA): You can use this BGA package as a solution for medium- to high- end applications. You will not need to use any external heatsink as it will provide exceptional thermal performance.
5. Package on Package (PoP): Do you want to save space on your PCB? If that is so, you should use this BGA package. It will permit you to put a memory device on some base device.
Micro BGA: This BGA package is quite small when compared with standard BGA packages. Currently, you will see 0.65, 0.75 and 0.8 mm pitch size dominating in the industry.
5、Designing PCB BGA
You may be encountering some challenges while designing PCB BGAs. In this chapter, we will describe the two strategies that will surely help you out.
You may be having problems in creating appropriate exit routes that don't result in assembly failures or similar problems. For right fan-out routing plan, you need to look into many PCB specifics, such as the number of I/O pins, pad and via size, trace width spacing, and how many layers are needed to fan out the BGA. Figure 6 illustrates exit paths in a BGA.
As a designer, it will not be easy for you to decide the number of layers of a PCB layout. PCB with more number of layers will be expensive. On the other side, you may need to increase the number of layers to reduce the noise level.
First of all, you should determine the size of the via, and space and trace width of the PCB design. Then, it is also necessary to determine the quantity of single-channel traces. After that, you should decide the number of layers that are required. For fewer layers, the key point is to reduce the application of I/O pins.
In the end, we would agree that it is not easy to design a BGA. You will need to follow certain design rules. As a beginner, you may find it difficult to design, but Altium Designer will surely make it easy for you.
6、Repairing Ball Grid Array
Replacing BGA with a new one is possible. You can repair or refurbish the BGA after removing it. It will come in handy if your chip is expensive. BGA repairing process is also called as BGA rebelling. In this process, solder balls are replaced. In the market, you can buy the tiny ready-made solder balls. They are specially designed for this purpose.
BGA devices have a major issue that you cannot view the soldered joints with optical methods. You cannot check the connections by only testing its electrical performance. There is a possibility that the connection is soldered inadequately, and with time it deteriorates. Thus, there is only one reliable method of inspection, i.e. X-ray inspection.
X-ray inspection will see through the soldered connections beneath the device. However, work has shown that BGA packages will solder without any problem if a solder machine is configured properly. It would help if you made your that heat profile is set up correctly. Figure 7 shows a BGA chip being soldered.
By now, you can right predict that reworking PCB BGAs is also not an easy task. However, with the right equipment, you can do it perfectly. In the PCB BGA rework procedure, a specific rework station is used to provide the heat required for removing BGA. That includes a thermocouple to control the temperature, a tool-holding with an infrared heater, and a package-lifting vacuum device.
You must proceed with great care and make sure that you are only heating and removing BGA. Moreover, nearby devices should be affected as less as possible. Otherwise, they will get burned. Figure 8 displays a BGA rework station.
In this article, we have explained in detail about PCB BGAs. How they can be the perfect surface mount technology for your ICs. What problems you may encounter and how to deal with them. You don’t need to visit any other website for any details.
However, if you still have any confusion, contact us at firstname.lastname@example.org. Our team of Engineers will be more than happy to answer your queries.