A few features to look for in a BGA rework station are pre-heating, an IR heat source, and the ability to focus and locally heat BGA components. Unfortunately, low-end vendors sometimes pass off units as IR rework stations when they are glorified hotplates. As far as serviceability goes, IR stations are generally the easiest to maintain. However, despite their ease of use, IR stations can be complex.
Choosing a BGA rework station
While considering several important factors when choosing a BGA rework station, you should not overlook a few factors. First, the features of a BGA rework station will determine how many PCBs it can rework at once and what kinds of jobs it can handle. For example, a machine without split-vision functionality will be best for basic jobs, and one that offers more complex functions will be most suitable for advanced rework jobs. Other factors to consider include accuracy and the quality of the rework.
Another essential factor to consider is temperature control. While some rework stations use traditional thermometers, a better option will feature closed-loop digital temperature control. This allows users to control the temperature and the measurement feeds back into the controller. The accuracy of temperature monitoring is essential when it comes to BGA rework. While most BGA rework stations are easy to use and maintain, some considerations are to make before buying a rework station.
Choosing a BGA rework machine is vital for several reasons. First, you should consider the number of BGAs you plan to rework and the size of the solder balls. A high-quality machine will also offer you the best quality BGA rework. With so many choices, choosing a rework station can be difficult. A good machine at Rayming PCB & Assembly will allow you to perform various tasks, including repair, refinishing, and qualification.
Choosing a heat source
There are many different heat sources for BGA rework stations, but some are better suited for certain types of boards and packages. For example, non-contact hot air excavation is best applicable for boards that contain sensitive components, like BGAs with lifted pads or impaired solder masks. On the other hand, robust PCBs often respond better to the heat from an infrared source.
There are several heat sources for BGA rework, including x-ray systems, SMT stations, and heat guns. The type of heat source you choose is essential because it will affect the solderability of BGAs. You must place a heat source correctly to minimize the risk of causing excessive heat migration. Having a well-developed profile and tight process control is key to minimizing the amount of heat migration. Furthermore, we can use a sophisticated x-ray machine to inspect beneath the BGA component to avoid excessive voiding or improper alignment.
If you’re new to BGA rework, it’s beneficial to take a course in the field. The hands-on training experience reduces the chance of significant errors in future rework. The Lorain County Community College, for example, is the first community college to offer an applied bachelor’s degree program in microelectronics manufacturing. It opened its BGA rework lab two years ago.
Infrared or hot air heat sources are two popular options for BGA rework stations. While hot air stations are generally more expensive than infrared ones, they’re ideal for reworking BGAs due to their even heat distribution and heat flow. However, both types of heat sources have advantages and disadvantages, so it’s essential to understand the differences before purchasing a heat source for your rework station.
Pre-heating a PCB
A well-functioning pre-heat is essential for successful BGA to rework, lead-free soldering, and CSP re-balling. Pre-heating prevents reworked boards from lifting traces, failing circuit tests, or scrapping. The following are some tips for pre-heating a PCB. First, let’s examine the benefits and disadvantages of a PCB preheater.
During the pre-heating stage, we slowly ramp up the assembly temperature from room temperature to 150 degrees Cdeg. This temperature ramp is regulated to maintain a constant rate, usually a few degrees per second. The soak stage maintains the temperature for a period to ensure that the entire board is evenly heated. The reflow phase begins once the board has reached the desired temperature, initiating the solder joint formation. This step burns off volatile solvents in the solder paste and activates the solder flux.
The heating profile for PCB rework is critical to the success of array-package rework. The temperature profile must be precise and must be continuous, and controlled. The rework station must have enough power and accuracy to pre-heat the entire board quickly. The reflow station should have a temperature control system with a hot-gas area heater. It should be able to maintain the component’s temperature accurately and continuously, preventing warpage and thermal shock.
Re-soldering a BGA
Re-soldering a BGA onto a PCB is a straightforward process. The process is like removing the device from its PCB, but you will use a different tool. Instead of re-soldering the chip by hand, you can purchase a special tool and print out a stencil to follow for the process.
Unlike RMA, water-soluble fluxes have a higher melting point than lead-based ones. However, this makes them more corrosive and aggressive than RMA, so thorough water washing is necessary after the reflow. In addition, when used on a BGA, a water-soluble flux can also displace the BGA, resulting in a white residue.
The reliability of a BGA solder joint is better than the reliability of the two other structures. This is since the BGA’s spot, and pad layers are “shaded” by the spot layer. In addition, cross-sectional X-ray detection technology can also detect hidden weld defects. Therefore, if the BGA’s solder joints are unreliable, it is recommended to re-solder them.
Performing a re-balling process involves the removal of a BGA component, cleaning the site, and attaching a new solder ball. Single-ball re-balling is rare but can add significant value to a BGA. However, this method is often difficult on assemblies that contain many ball joints. Also, some ball pitches are too small, and many balls may not be able to be repaired.
Avoiding common mistakes
There are many common mistakes in BGA rework, but there are some steps you can take to minimize the damage and save time. Of course, using the right equipment is critical, but learning from others can avoid some common mistakes. For example, one common mistake is using the wrong type of solder paste for the job. This will result in the solder joint voiding, but it will also compromise the points where the solder attaches to the BGA.
A poorly-developed thermal profile is another common mistake in BGA rework. A poorly-developed thermal profile will result in the BGA component becoming damaged and causing adjacent components to reflow. Tight process control and an excellent thermal profile are essential to minimizing heat migration. In addition, using an x-ray machine will help you inspect the BGA assembly and detect any defects in its alignment or placement.
When using a BGA rework station, make sure that you select one that has cooling capabilities. Since BGAs tend to be very hot, you want a station that will minimize the amount of heat generated. Moreover, you should choose one suitable for the type of PCBs you’ll be reworking. For example, older PCBs need a lower temperature while newer ones need higher temperatures. Additionally, make sure the PCB size and holding capacity fit into the station’s limits.
