BGA Rework Station

Temperature Control of BGA Rework Station Is Very Important

The rework stations with the most user-friendly designs are those that come equipped with precision heaters at the top and bottom. With this design, you can keep the temperature consistent along both ends of the PCB. Hot air rework stations will typically employ focused heated air on the top and an unfocused board heater for the lower portion of the heating area. The flow of air will heat over the BGA and under the board as well. The bottom part of the heating compartment will consist of either a plate heater or an infrared light heater. On certain models, the plate will be equipped with holes that allow for the passage of heated air. If the area that you intend to heat is small, you may need to place the area directly above one of the holes in the plate from which heat emits. It might even be necessary to mark the spot where the PCB has been placed. If the hole and the spot are not properly aligned, the solder could be warmed to the wrong temperature. Additionally, rework stations should be equipped with a software program for setting temperatures and adjusting the temperature for each of the heaters to the exact degrees necessary for the project at hand. If properly designed, the rework station will calibrate the software temperature setting and the temperature of the heat that comes forth from the nozzle. The main problem is that the underside air is unfocused, which makes it difficult to guarantee an even spread of heat between the top and bottom of a given board. Without any feature that will focus the air along the bottom of the PCB, you might need to manually adjust the temperature along the underside of the heating compartment. The underside heaters on IR rework station models are designed with no bottom-side focus for the heated air. Some IR rework stations use a heat light equipped with a black diffuser that makes it easier to heat the circuit board evenly from one end to the other. Due to the inability for the software to calibrate with the heat on the infrared under-heater, there can be a temperature variance as wide as 100° C in certain units. On certain models, the software will not even allow you to set the heat in degrees. Instead, you are only allowed to set the heat in percentages, which can make settings even more difficult to set properly. You may need to place thermocouples on the printed circuit board and check the temperatures frequently. As you first get the process down, some of the chips are liable to wind up fried.

Key Features to Consider When Buying a BGA Rework Station

Hot air BGAs apply air with a pump. Consequently, hot air rework stations typically produce some degree of noise. Newer models are usually equipped with quieter pumps, though the sound issue is still a factor that you must accept if you use this type of rework station. IR stations usually produce no noise at all. If you need to limit the amount of noise that comes from your rework machine, an IR station would be the better option. Noise can be an issue in certain settings, especially if there are already several loud machines going at once. Hot air rework stations are equipped with nozzles that make it easier for users to focus the flow of air on different areas of a printed circuit board. When the process is conducted by a skilled set of hands, the task can often be completed sooner with a hot air BGA because such units make it easy to isolate the more delicate details that can be hard to heat. With a focus beam IR, you do not need to buy heat nozzles of different sizes, since each beam can refocus at your command. However, it will often take longer to bring more delicate details to the desired temperature. Sometimes the IR beam cannot heat the lighter details on a ball grid array. A particular problem area with IR beams are the silver spots on a BGA, which often need black tape to bring them to the necessary temperature. Additionally, your success rate with a rework machine will all depend on whether the unit is sufficient for the volume of reworks you hope to achieve in a given day. The best BGA rework station for high volume work will generally be of the heated air variety. A hot air station makes it easier to heat the solder and complete the job sooner. Hot air machines have more parts and accessories since you need different sized nozzles. This can make them more complicated to repair and maintain. IR BGAs consist of fewer complex parts, which allows for less complicated maintenance and repairs. On the downside, these units run the gamut in terms of quality, as some of the low-priced models are typically equipped with low-grade parts that offer subpar performance. When it comes time to perform a more complex set of tasks with a lower grade IR rework station, extra tools will often be required. You should also consider the frequency at which maintenance is liable to be necessary for the respective unit. If a rework station consists of numerous complicated parts, the likelihood of a breakdown could be a real and costly threat. If the rework machine consists of a minimum of parts yet offers excellent results, you have probably found the best rework station. Another important feature on a reworking station is an automatic cooling fan. With this feature, the printed circuit board and each of the heaters in the machine will all be cooled when necessary. As you work on one PCB after another, the unit will automatically cool as needed between each board. A cooling fan is essential for project efficiency on most reworking stations, which tend to cool slowly between applications. BGA machines that use drilled metal plates can take especially long to cool. The size and sensitivity of your boards can also affect which type of rework station is best for your operations. Some machines can hold boards up to 36 inches. The space within the heater should accommodate the circuit board well enough to bring the entire PCB up to 150° C. This should help offset any possible warping effects. The age of your boards may also affect which machine is best. Over the past two decades, lead-free soldering has become the new standard in manufacturing. Consequently, reworking requires higher temperatures on newer printed circuit boards. On older PCBs, less heat was required for reworking because tin-lead solder melts at lower temperatures. If you work primarily with newer PCBs, you may need a more powerful station that can achieve higher temperatures.

Operation Principle of BGA Rework Station

Professionals who have done BGA rework station work know that "warming up" is the prerequisite for successful rework. PCB processing at high temperature (315-426°C) for a long time will bring many potential problems. Thermal damage, such as pad and lead warping, substrate delamination, white spots or blistering, and discoloration. The "invisible" damage to PCB caused by high temperature is even more serious than the problems listed above. The reason for the huge thermal stress is that when PCB components at room temperature suddenly contact a soldering iron with a heat source of about 370°C, a desoldering tool or a hot air head to stop local heating, there will be a temperature difference of about 349°C on the circuit board and its components, resulting in "Popcorn" phenomenon. Therefore, regardless of whether the PCB assembly plant uses wave soldering, infrared vapor phase or convection reflow soldering, each method generally requires preheating or heat preservation treatment, and the temperature is generally 140-160°C. Before the implementation of reflow soldering, a simple short-term preheating of the PCB can deal with many problems during rework. This has been successful for several years in the reflow soldering process. Therefore, the benefits of stopping preheating in the prevalence of PCB components are manifold.