A Ball Grid Array (BGA) is a packaging for surface mounting of integrated circuits. BGA packages have more interconnection pins than a flat or dual inline package so they can permanently mount devices such as microprocessors. BGA rework is the repair or refinishing operation of a BGA. We desolder and then re-solder the surface-mounted electronic components. Batch processing cannot repair a single device. Hence, we need expert personnel who use appropriate equipment for replacing defective components. We use a hot air station or a hot air gun for melting solder and heating devices, and then we use specialized tools for picking up and positioning tiny components. So, BGA rework is more cost-effective than the manufacturing of new BGAs. Hence, this method is favorable in the industry.
BGA Rework Process
We need a dedicated setup if we use BGA rework for industrial applications. BGA rework requires Highly skilled and well-trained personnel who know how to work with sophisticated tools. The steps involved in a BGA rework are,
1. Component Removal
A BGA rework needs preheating before the removal of any component. We apply localized heat from the top of the component and the solder melts. Then we remove the component from the BGA via a vacuum.
2. Site Dressing and Solder Removal
This step requires fixtures for holding the component down while the exposed solder is faced up. Then the component is kept flat by the vacuum from beneath, and vacuum on the top allows for removing the residual solder.
3. Component Attachment and Re-soldering
Once we have removed the components and cleaned the sites, then the next and final step is re-soldering. In this step, we reattach repaired or replacement components to the BGA by using soldering. A complementary technique is solder dipping, where we dip the BGA into a pre-determined soldering fixture.
Common Mistakes of BGA Rework
BGA rework is mainly dependent on science, but art plays a major role as well. The operator must have deep knowledge of the rework phenomenon and skilled hands for handling delicate components. This makes BGA Rework one of the most difficult and challenging industrial procedures.
Here are six common BGA Rework mistakes which you must avoid,
1. Inappropriate Operator Training
We can’t emphasize this enough. BGA rework technicians should have a lot of experience, have appropriate training, and developed skills. A BGA rework technician must understand the tools, the used material, the process steps, and the parameters involved. The technician must be able to evaluate the progress of a BGA rework and scale it accordingly. He must be able to recognize the indications of the process being off-track.
2. Inadequate Equipment Selection
You must use the right tools for doing a perfect job, and the same goes for the BGA rework. The equipment must have the desired flexibility and sophistication. It should allow for sustaining a predictable, repeatable, and controlled process.
This includes the robustness for delivering heat as required by the process, closed-loop thermal control and sensing, and handling abilities for replacement and removal. So, you must use the best equipment available because it is directly related to the quality of a BGA rework.
3. Poor Profile Development
The BGA rework profile is very important, and you won’t be able to attain a repeatable and successful BGA rework process without it.
A poorly-developed thermal profile can lead to damaging the BGA assembly or components. This can lead to requiring additional rework cycles, which can be very costly. Hence, the operator must develop excellent profiles with the utmost care by using the correct placement of thermocouples and analyzing the data provided by them.
4. Improper Preparation
We need a lot of preparation before the application of the first heat cycle to the rework site. This includes removing moisture from the BGA assembly for preventing subsequent problems and removal/protection of adjacent heat-sensitive components for avoiding inadvertent reflow or damage.
We need to make many decisions in advance, which significantly affects the BGA rework. These include whether or not to use solder paste, selecting the correct solder paste stencil, and selecting the right chemical compositions and alloys.
We need to appropriately set everything in place before the initiation of actual rework cycled. These include an accurate evaluation of the solder ball size, ball and device co-planarity, taking care of solder mask damage and contaminated pads at various sites.
5. Collateral Heat Damage
Reflow of adjacent component solder connections may result in de-wetting, lead and pad damage, oxidation, starved joints, wicking, component damage, and other problems. This may lead to numerous rework issues.
The BGA rework operator must be the effect of heat on the BGA device and adjacent components at all times. The objective here is to minimize the migration of heat beyond the BGA component under rework. This depends on tight process control and a well-developed profile.
6. Insufficient Post-Placement Inspection
It is difficult to observe what lies beneath a BGA component with the naked eye. But today, sophisticated x-ray machines are available, which allow us to see below the BGA component. This helps in avoiding problems like poor placement, excessive voiding, and poor alignment.
An x-ray system operator needs proper training for correct understanding and interpretation of the generated image. The complexity of the BGA component and the x-ray image variants demand that we obtain maximum benefits from this sophisticated equipment.
BGA Rework Stations
There are two main types of BGA rework stations,
1. Hot Air Stations
2. Infrared (IR) Stations
The main difference between them is the way they heat a BGA.
Hot-air rework stations use hot air for heating the BGAs. Nozzles of varying diameter direct hot air on the area of the circuit board, which needs repairment.
Infrared (IR) rework stations use infrared precision beams or heat lights for heating the BGAs. Ceramic heaters are used by the low to mid-tier IR rework stations, and they use louvers for isolating the areas of focus on a BGA. The upper-tier IR rework stations use focus beams, which provide better isolation to the BGA without causing heat damage to the adjacent regions. We can focus the beam with varying intensity and scope on various areas of the BGA.
How to choose the right BGA rework station?
Both kinds of rework stations have their pros and cons. To decide whether to go with hot air or IR for your company, you must consider both their features and take into account how they will perform in your work environment.
You need to factor in the following parameters when deciding on your BGA rework stations,
1. Temperature Control
Hot-air rework stations usually focus heated air on the top and use an unfocused board heater for the lower portion. The airflow will heat over the BGA and under it, as well. In certain rework stations, the plate used for heating of the lower portion has holes that allow for the passage of heated air.
The IR rework stations don’t include a bottom-side focus for heated air. IR rework stations typically use a heat light equipped with a black diffuser that makes it easier to heat the BGA evenly.
The hot air rework stations have nozzles that allow for focusing of airflow on different areas of BGA. If the operator is skilled at his job, then he can complete the task quickly. Because the hot air workstations make it easier to isolate the delicate details which are hard to heat.
IR workstations don’t need nozzles as each beam can refocus as per the operator’s command. But it may take longer to bring more delicate details to the required temperature. As IR workstations are very sophisticated; therefore, the staff needs to be better trained, and employees will need more time to develop the required skills.
3. PCB Specs
The sensitivity and size of your BGAs will also affect the kind of rework station, which will be more suited to your operations. Some rework stations can hold BGAs up to 36 inches.
The space within the heater should have enough room to accommodate the BGA such that the temperature of the entire BGA can be raised up to 150° C. This will help in offsetting any prospective warping effects.
The age of the BGAs being used will also affect the kind of rework stations you should choose. In the last two decades, load-free soldering has become the standard practice. As a result, we need to rework the BGAs at higher temperatures. Older BGAs need less heat for reworking because they used tin-lead solder, which melts at lower temperatures. If the rework involves new BGAs, then you will need a powerful rework station that may achieve high temperatures.
Effective BGA rework requires a high-end setup, a sophisticated work environment, and a well-trained operating staff. Many manufacturing companies don’t have the capital or resources for arranging these and end up producing poor quality BGAs. The smart way to address this is to reach out to a company like MOKO Technology, which only manufactures PCB and PCBA but also specializing in BGA rework. Our operators are highly skilled and well-trained, which allows for a greater degree of customization. Hence, we will tailor our BGAs to meet your specific requirements. Feel free to contact us if you have any further queries or if you would like to ask for a potential quote.