A ball grid array is a surface-mount package for integrated circuits that is used to mount devices. The BGA’s bottom surface is covered in pins arranged in a grid pattern, hence the technology’s name. Instead of being wire pins, these connections are made with pads with balls of solder. These connections need to be carefully soldered due to their location underneath the package.
Once the solder connections are complete, however, they are no longer visible to the casual observer. Because they are not visible, more advanced inspection techniques are required to ensure their quality. This is where BGA inspection plays a vital role.
BGA inspection is a process where the connections between a chip and a PCB are analyzed to ensure quality. BGA inspections look at various aspects of the ball grid array, including the package’s standoff height, the quality of the connections and more. In BGA inspections, unassisted visual inspection is extremely limited, so other techniques are required to get a detailed look at the connections.
These analysis methods include electrical testing, assisted optical inspection and X-ray inspection. The components of these techniques will be discussed in greater detail further along in this article
Why is BGA inspection important?
BGA inspection is notoriously difficult for one reason — the solder joints are located beneath the BGA package. Because of this feature’s positioning, it can be challenging to get a good view of the BGA for inspection. Despite this difficulty, inspection is essential for BGAs for several reasons, including:
- Soldering difficulty: Soldering BGA components is tricky, as it requires sufficient heat to be applied to the array so all balls in the grid melt sufficiently to make solder joints. Both the density of connections and the difficulty of soldering mean there is a high likelihood of a defect occurring. Inspections help experts catch these defects so they can avoid sending out faulty parts.
- Unreliable electrical tests: Electrical tests run a current through the PCB to ensure it is electrically sound. However, this type of test can only judge whether the current is on or off when the BGA components are connected. These tests are not reliable as they can only find a handful of defect types and cannot pinpoint the locations of any defects they find. Comprehensive inspections that combine this method with other techniques can create a more complete overview of errors and their locations.
- Material reuse: If a BGA is found to have a solder defect, it can be removed using a rework station and replaced or refurbished for reuse. The inspection process identifies defects early on so materials can be saved in this way, which reduces material waste.
- Quality control: BGA SMT assembly relies on quality physical connections, so BGA quality control must include a detailed inspection of these connections. Inspections can also identify common defects and patterns. These are important, as repeated defects may indicate issues with the manufacturing and assembly process or even the product’s design.
- Cost reduction: Thorough inspection processes minimize the number of defects that pass on to the next stage of production. Defects that pass inspection may get caught further along in the production process, making rework more costly. The later the defect is caught, the more expensive it will be for your company. That is why early prevention and resolution is crucial.
Because of the importance of inspection, inspection teams must utilize thorough and effective tools and techniques in the process. That way, these teams can catch all issues and pinpoint their locations and causes before they become bigger and costlier problems.
What are the common defects of BGA?
Due to the BGA’s complexity, many potential defects can occur during the soldering process for a BGA. Some problems that may arise include the following:
- Misalignment: Misalignment happens when the PCB and BGA are offset during reflow and connect at incorrect points. This is one of the most common issues that occurs during BGA assembly.
- Inconsistent standoff height: BGAs are set on top of PCBs, and improper soldering can result in the BGA setting at a crooked angle on the surface of the PCB. This asymmetric standoff height can compromise the security of connections.
- Missing balls: If balls are missing from the BGA when it is attached to the PCB, essential connection points may be missing from the assembly.
- Non-wetted pads: In some cases, reflowed solder paste may not wet the pad correctly. This may result from incomplete reflow or leftover solder resist from previous steps in the production process.
- Bridges: Bridges occur when extra solder paste is left between paste deposits. Bridges between connection points often result in shorts.
- Partial reflow: In some cases, the reflow may not completely cover the board. This often occurs because of insufficient solder reflow, human error or mechanical malfunctions.
- Popcorning: Popcorning occurs when balls merge together during the soldering process. This is a common problem for BGA and, like bridges, results in shorts.
- Open circuits: Open circuits occur when solder fails to wet the PCB pad and climbs onto solder balls and onto the component surface. While an electrical test can identify this as a problem on a board, it cannot identify the cause of the issue.
- Voiding: Voiding occurs when flow stops short of a solder connection. This is a common problem in collapsible BGA components.
These issues can all be fatal errors for the final product, so catching them with quality inspection techniques and technologies is a necessity. Fortunately, modern inspection techniques have advanced to a point where most of these defects can be identified using one or more inspection methods. However, it is also essential to avoid these defects wherever possible before assembly.