Choosing a BGA rework station Hot Air vs IR
Hot Air is older technology, having been around for more than a decade. IR is relatively new technology in the reworking market which can include Short, Medium, and Far wave lenghts.
Hot Air Rework Stations tend to have the fault of uneven heating due to PCBs being unevenly populated with components. IR provides more even heat due to absorption rather than penetration thus a simple benefit of IR is it can remove plastic components, such as a CPU socket, with IR it penetrates the solder joints and does not burn or melt the plastic. IR Rework Stations are typically silent in operation because there is no air flow, while Hot Air Rework Stations uses a pump to force air through the system which is then heated.
There are nozzles that have been designed so that they make contact with the PCB to help with providing even air circulation and heat distribution. These types of nozzles would have vents to allow the air to escape. However these nozzles can not be utilized properly when components are near the package. Thus a disruption of proper air cirulation would occur and cause uneven heating. The air that escapes the nozzle may also heat adjacent components and may even burn plastic components or blow small resistors and capacitors away.
From a manufacturing standpoint a Hot Air Rework Station is more complicated to manufacture than its IR counterpart as a result its manufacturing cost is higher. This is because it requires more internal wiring, different sized nozzles as well as a forced air pump and fan system. The use of nozzles in a Hot Air is required which has both a pro and a con, the con is you have to purchase different nozzles for different sizes of chips and the pro is that nozzles can be rotated in 360 degree which is very easy for alignment.
IR stations tend to use ceramic heating plate, they give even heating without causing shift of other surrounding components due to the lack of air movement, but due to the IR plate being a fixed size, you may need to use high temperature tape to cover the surrounding area of the BGA chip. When using Hot Air you may come across this same issue if your nozzle is not an exact fit or the air flow is too high.
Many of the expensive Rework Stations use Hot Air because well its been around longest and many companies do not want to switch. They have procedures in place and changing them all as well as retraining all operators will be very expensive. Samsung or Intel with several millions of employees having to retrain and re certify them is typically not a priority for them. Why do you think so many companies still use Win 2K or XP, its all about the transition cost and time.
IR Rework Stations are newer and not as popular, but they gaining much more interest, the main reason IR is associated with being a terrible technology for reworking is due to the inferior ceramic heaters being used in the cheaper popular Rework Stations. Higher end Rework Stations such as those fitted with Elstein heaters will perform much better. 99% of game console and laptop rework technicians have used or are currently using a cheap IR Rework Station made in China, probably from common brands such ACHI, Scotle and LY due to their affordable price. There are very expensive high quality IR machines many of them using focused IR such as PDR which is an extremely powerful technology but for the average reworker these units are far too pricey.
Regarding the ACHI machines, it was a brand targeted to be very cheap and that it is, it works but needs lots of user experience as well upgrades to make it work well. The Jovy RE 7500 is targeted to mobile phone reworking and small components thus it works well for that, but many technicians used it for large PCBs and chips which caused problems most of which were in relation to board warpage or flex thus they blamed the Jovy Rework Station and feel it is inferior. Realizing this, Jovy released a newer model of their popular 7500, the RE 8500 which eliminated most if not all of the previous issues. This model is nowhere near as cheap in price compared to the other Chinese brands as it comes stock with Elstein heaters.
A very recent BGA Rework Station called The BGA Rework Machine is made in the USA performs extremely well. This BGA machine is offered in 2 zone and 3 zone full IR.
Any person can perform reworking with just about anything. Anything from an open flame to a million dollar rework station. Heat guns, SMT Rework Stations, BGA Rework Stations, torches, stoves, ovens and more can all be used as heat sources. Understanding the heat source, using it properly and ensuring that its the right heat source for the job, is where many fail. Many rework technicians attribute their setup as being successful. Having success in regards to any amount for example 60% success rate or even 30% gives the user confidence in themselves and their process.
Reworking is a science, its not just about heating things. Simplistically it can appear to be that is all that is do, heat the chip and remove it. There are many variables involved. MSL or moisture sensitivity level, package size and type, environmental variables, pcb thickness and quality, copper planes, flux, solderability and more.
User A can rework a board and have it working in 9 mins with $500 setup. User B can rework in 3 mins with $40,000 setup. Both boards work from both users. Both feel they have success, but there are more variables involved. User A board may last a shorter or longer period of time than the board repaired by user B. Equipment and user are the biggest factors in reworking. User A may fix 60% of boards and they last 6 mo. User B may fix 90% of boards and they last 2 mo. User B may feel over confident and not use proper profies thus causing many problems.
Variables that affect User B may not be the same for User A thus having less success but longevity. The success rates can also change if the user does not update processes and monitor variables. The same principles can be applied to a chef, chef A is a veteran and has a dull knife, chef B is a noobie but has a very sharp knife. Chef A or B could have a better cut with their current setup, but if the 2 switched setups chef A would most always have the better cut while chef B would blame their setup for the lack of success.
Using several types of equipment at XModdz, i can honestly say Hot Air is geared towards smaller components since it is able to be focused using nozzles. IR can be used well with large BGA due to the heater being very large itself. The Aoyue 732 uses Hot Air & Quartz IR, basically air is pushed through the IR plates thus providing heated air as well as convection or radiation to the board. When reworking smaller components the provided nozzles work fine since the thermal mass is low there isnt a lot of problems with uneven heating. When reworking larger BGAs, the nozzles in place would not work well as there would be uneven heating issues, i would remove the nozzle and raise the heater when reworking RSX chips and the temps are usually spot on, the downside is it takes longer to heat since the air flow is not being focused but having an even heat spread more than makes up for that. For smaller BGAs the nozzle in place and low to the component suffices.
Package temperature is also very important, non ROHS, PB, or lead packages would tolerate a temperature of around 235c, while ROHS, PB free, or lead free packages tolerate temperatures of around 260c. New processors and chipsets use integrated heat spreaders or IHS. It is a heatsink that is affixed semi permantely to the chip. When reworking an RSX chip with a Hot Air Rework Station the package temperature would be much higher than the solder ball temp and this is due to the penetration technology heating up the RSX since it is closer to the heating source and was absorbing much of the heat, applying heat resistant material such as Kapton or Aluminum tape to the IHS reduced the temperatures considerably. When reworking with IR the package temp was very close to the solder ball temp due to the absorbtion characteristics of the PCB and the reflective coating on the IHS.
Using the ACHI with the stock heating elements is essentially a terrible idea for multi layer boards. Not to metion the heaters are usually overpowered and effectively will degrade much quicker. During our testing which involved upgrading all 5 ceramic plates with Elstein heaters we noticed there is a much more evenly controlled spread of heat. Reworking thinner boards such as cell phones using the stock ceramic heaters worked fine, but larger boards were an issue. Sometimes using the top fan would help with evening out the heat, in some cases it did not make a difference.
With the ZX 360 station, things were much more complicated and took a very long time to setup, it used a more complicated control system where there were many different settings to be in place. Also having come from IR to Hot Air getting used to the air flow system took some time. The recommendations for this machine is to have the nozzle very close to the board almost touching it and this is due to the nozzle design. The nozzles design featured a vent on each side which allow for the heat to be released after penetrating the component instead of creating an extreme environment. This is a common design on high end Hot Air rework stations.
I will end by saying i prefer IR technology over Hot Air. Companies continue to use and purchase Hot Air Rework Stations and that is simply due to cost In order to retrain all their staff, update their policies and procedures in order to use IR would be an enormous expense to them despite the improved technology. Think of how many companies are using Windows XP to this date, because of the transition costs and retraining they simply refrain from upgrading. I can without a doubt say IR technology is much easier to use than Hot Air. With our IR systems simple modifications of the heating temps for thicker/ thinner boards in the profile was all that needed to achieve a proper rework. Using Hot Air, there was much more involved, raising or lowering the heat, adjusting air flow as well as having longer dwells and increasing the number of profiling steps to achieve a proper rework.