So I have decided to build a DIY BGA reballing station to replace T61 video cards and X230 processors.
Disclaimer: I will tell you what I do. If you choose to do anything similar do it at your own risk. Do not attempt anything unless you're fully qualified to build and use a high-wattage appliance running at 240V producing large amounts of heat. Do not leave the device unattended. Temperatures may raise well above combustion level for wood/paper/wires and household items. The machine may pose among others a high risk to health life and property from electricity heat and fire!
Background: people have been repairing computer motherboards probably for as long as home computers existed. The process I believe is similar to those performed at phone repair shops around the world. While replacing components with 2 or 3 connections to the PCB is relatively simple replacing a large BGA chip like graphics card or a CPU is a much bigger task. The process that people arrived at is to
- heat the motherboard from the bottom (hmm a little usure to what temperature?) to probably around 160C? using so called bottom heater
- then heat up just the chip being removed or soldered on to the board from above using so called top heater
A crucial point here is that many people have observed is that it poses the least risk of damaging the motherboard to heat it
all up all and do so evenly. In practice the edges will probably be colder than the middle but we can still try to make it as even as possible. The reason to heat it evenly is to avoid the risk of the motherboard getting crooked after the process.
This brings us to the following rather unoptimistic conclusion: the bottom heater ideally needs to be slightly bigger than the biggest board that you plan to work on. Bigger bottom heaters are a problem. For me it's a problem where to store it - I only plan to use the device very rarely. The other problem is power - the bigger the bottom heater the more power it will consume. I have been advised that ideal power ratio for bottom heater is between 2.5 and 3.5 Wt per square centimeter. I've also been advised that a 800Wt top heater is a common thing to build. Now the wires in residential apartments and sockets have their limits.. I have decided to limit my power consumption to 15A. Yes most of the time the heater is not working at full power. Yes normally when top heater switches on the bottom one is already running at partial power. Yet I would want the total theoretically possible power draw not to exceed 15A. 15A at 220V is 3.3kWt. Take away 0.8kWt for top heater and you only have 2.5kWt for the bottom one. Not that much really.. I heard from one guy he built a 20*25cm bottom heater and found that insufficient. He said ideally he'd wanted a 30*40 one
Not sure what he wants to solder though.. my bottom heater has to be large enough to cover T61 motherboards - not that big really and X230 motherboards - not big either. 25*30cm would be enough for either. But then just in case I would want to cover motherboards of modern Thinkpads like T480. These are narrow but rather long.. Hmm..
The chips that I'd like to replace are relatively small say 31*24mm. Interestingly it seems the general advice is that I still need a rather large top heater.
This forum post has interesting pictures under it. The left shows some kind of thermo-paper heated up by a 60*60mm top heater from 5cm distance. It shows this heater just barely heats up more or less evenly a circle with 35mm diameter. The right image there shows heat distribution ELSTEIN SHTS/100 800W. Not sure how high the heater was above the test surface but probably about same height as previous test. The legend explaining: "circle El1 has diameter of 4cm and 5C difference between centre and edges; circle El2 has diameter of 5cm and 10C difference between centre and edges; circle El3 has diameter of 6cm and 15C difference between centre and edges". I've also been advised that the evenness of heating from top heater can be improved by moving the heater further away from the surface of PCB. But it requires the area and power to increased. I have concluded I may need a 10*10cm or maybe even 12*12cmd top heater. Maybe 8*12cm.
To be honest many people succeeded in replacing the chips with much more basic equipment. They used bottom heaters that don't heat the whole of the motherboard. They used heaters which didn't heat it up evenly. They used hot air instead of top heater to de-solder and re-solder. In my understanding using a more proper station with accurate temperature control and big top/bottom heaters should yield a higher chance of success. I'd like to essentially compensate my total lack of skill with better equipment.
There are 3 basic options for bottom heater:
- an array of tube lamps (possibly normal halogen light ones run at 1/9 or 1/4 power or specialized heater lamps)
- an aluminium board of sufficient thickness painted with heat resistant black paint + MCH heaters:
video; the author of this video refers to his station as "Thermobro"; I heard you don't really have to use that fireplace tape that looks like webbing he's using in the video between MCH heaters and the board; I heard one can use regular thermal paste instead; I also heard
this TaoBao shop may be a good place to get MCH heaters - but depending on where you are you may need to use an intermediary like superbuy.com to get the money in and goods out of China
- ceramic panel(s) made specifically for this purpose
Similarly for top heater there are two basic options:
- lamps in appropriate arrangement
- ceramic panel made specifically for this purpose
Not at all unexpectedly heaters based on lamps are easier to control. The trick with working with PCB-s on such a station is to do the heating at a controlled speed - not too fast and not to "overshoot" - not to allow the temperature to go above the set targets. Ceramic/aluminium heaters have more inertia - even after you remove power they remain heated up and continue emitting heat. Therefore in order to avoid exceeding heating speed and in order to avoid overshooting the firmware in the controller needs to be more considerate and think more in advance. Apparently it is possible. However because I want to make my life simpler where possible I have personally chosen to use lamps. Their inertia is pretty small - you remove power and they stop radiating that much heat more or less immediately.
Another interesting topic is what to cover the bottom heater with. One option is to cover the lamps with some kind of a wire mesh - to prevent things from accidentally touching the lamps. Honestly I haven't found a good source of such mesh in the UK yet. If mesh is used some kind of supports are needed to hold the PCB in place over the bottom heater. Placing the supports directly on the mesh didn't work that well for people - the mesh gets deformed from heat.
The other option is to cover the lamps in the bottom heater with a ceramic glass - such as those used on ceramic cookers. Not on inductive ones, but those which heat cooking pans with IR. The advantage of using such a glass is that apart from being aesthetically appealing and removing excessive light from the bottom heater lamps it allows one to place the PCB directly on top of it with the help of some minor PTFE stands. It's rather convenient. I decided that I want to try the glass.. I can always throw it away if it doesn't work for me.. I've even seen people cover the top heater once with a similar glass on youtube.. Apparently cutting this glass shouldn't be a big problem. I have a battery powered Dremel and with diamond cutting disks like
these it's said to be possible to cut such glass. The trick apparently is to have the wcontrol and with large enougorkpiece covered with a couple mm of water (here's why it's important that my Dremel is a battery powered one: no fear of working with water!). I have spotted one nice part-broken glass on ebay but it's around Liverpool area and I'm on the outskirts of London. And it's a pick up only item.. So I will probably give up on that glass and try to order
this one from China. Only 4mm but about the right size.
My main source of information is
this thread on a Russian forum of Arduino hobbyists but also other websites and private conversations. Interestingly enough there seems to have been quite a number of such stations built and discussed in Russian segment of internet. I will probably never have enough time to read all the online discussions
The forum topic I linked to is an active ongoing project where people are writing firmware for such stations powered by Aruduino Mega 2560. As things stand now the sources are not placed under a version control system such as github. Instead the sources are attached as .zip files to forum posts. There is some lack of clarity around the license for this code shared online. Lastly the UI that this project is displaying on a small 4" screen attached to Arduino is in Russian. My own project has got two goals: build the station and help the guys get their code somewhere around github. If this happens I hope to contribute to the project a little adding some docs in English and implementing an option to have the UI in English. We'll see how successful I am in these endeavours.
My initial plan is to make things simpler for myself so at the moment I'm buying exactly same parts as the guys on Russian forum did. The idea is to use their firmware directly. The parts I have ordered from China will take a long time to arrive so I don't expect to be making a lot of quick progress on the project. I may share what I ordered a little later, though I don't have full confidence I have ordered the right parts. I have also ordered some generic soldering equipment and that may also take quite a while before landing my doorstep.
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