Microsoldering Repair Tutorial For Beginners

Microsoldering School, Day One: You’re Heating the Board, Not Just the Components

Day one was mostly theory. We learned which end of the iron to hold and how to treat second-degree burns. No not really, but we did learn some fundamentals. This included a very brief introduction to Ohm’s Law and the relationship between voltage, current, and resistance. It’s an invaluable principle to understand, especially when it comes to figuring out how to safely use a variable power supply.

We also learned about schematics, something I had apparently misunderstood the purpose of for years. Aside from enabling repair, I mistakenly thought these were the blueprints for reproducing a device. That’s definitely not the case. No matter how hard manufacturers try to argue it, you cannot make an iPhone clone by ordering the individual integrated circuits (ICs) from the schematics. What a schematic can do is provide us with a guide on how components are connected. It’s a map we can navigate. It’s more like the wiring diagram of a house instead of the house’s blueprint.

This means that we can use schematics to backtrack from the symptom of a failure (say we have an iPhone 14 that won’t charge) and trace all the circuits that might be relevant to this failure back to the source. The problem might be a ripped contact, a broken line on the printed circuit board (PCB), or a damaged IC, among a whole host of other things. If it’s a blown charge IC (Tristar in the older iPhones and many current generation iPads) then we can quickly find where it’s located. If it’s not Tristar, the schematics allow us to trace a route further up the circuit so we can figure out where the failure point is.

Unfortunately, the chances of finding schematics for most repairs are very slim. Most manufacturers simply don’t release schematics for their devices anymore. Hopefully that will soon change: Right to Repair laws that have passed in US states including New York, California, Oregon, and Colorado require that manufacturers provide “schematic diagrams.” But so far, to our knowledge, only Fairphone has fully complied. Rest assured that we’ll keep pushing manufacturers to make available all the documentation you need to do repair, microsoldering included.

Without schematics, we have to solely rely on other skills, like taking multimeter measurements in diode mode to identify a fault. I’ll get into more detail about taking diode measurements and interpreting the readings in the next post.

After we talked some about this theory of microsoldering, I expected we’d break out our soldering irons and get to work, removing ICs from iPhone boards. But Jessa had news for me. Unlike in through-hole soldering, where you remove a component from a board by heating up the individual solder point, a microsoldering repair usually has to start with broader heat than you can get from a soldering iron. So most microsoldering starts not with a soldering iron but with what’s called a rework station, which is somewhere between a soldering iron and a heat gun. It blows a concentrated stream of really hot air.

The last lesson of the day centered around the rework station. The rework station is your best friend when dealing with surface-mount devices (SMDs)—that is, components that are mounted onto the surface of a board, not stuck through it as in through-hole soldering. In a modern smartphone or laptop, everything—from resistors and capacitors to memory and the system-on-chip brains of a device—is surface-mounted.

SMDs often have dozens or even hundreds of individual solder points. Where a soldering iron can apply heat with pinpoint accuracy, the rework station spreads that heat over a wider area to manipulate multiple solder points.

The amount of heat applied and how fast the heat is applied will be the key to success when using the rework station. You need enough heat to melt the solder under the IC but not so much that you end up frying the chip and melting the PCB. It’s easy once you understand how much heat you need and how that heat travels through your work surface.

Let’s start with the solder. We know that the melting range of leaded solder will be around 183C (361 Fahrenheit) and led-free solder around 217C (423 Fahrenheit). Most of our electronics are now made with lead free solder and that’s certainly true for the iPhone. So you’d be forgiven for thinking that if we set our rework station to 217C, that would be enough to remove any single chip on a PCB.

Except it’s not, our ICs are soldered to layers of copper sheet. Copper is very good at conducting heat, it’s one of the key characteristics that makes it an excellent material for use in electronics. Now imagine what would happen if we applied heat to the iPhone 6 touch IC while suspending the logic board in a vise.

That heat is going to diffuse through the board quickly, meaning the touch IC we want to remove won’t hit 217C until the rest of the board also reaches 217C. We don’t want that. Aside from the fact that all the solder points on the logic board would liquify—including the ones underneath the board that will drop away under the force of gravity—there’s a strong likelihood that we’re going to damage both the PCB and the ICs under prolonged thermal stress.

The solution? Apply heat more quickly than it can diffuse across the board. In this case it meant I had to crank the temperature up to 380C and my air to about 60 (60 what? I have no idea. Let’s call them 60 air zoomies for now).

It’s fairly easy once you know what temperature settings are appropriate, something that comes with practice and experience.

One thing I noticed immediately was how each person found a temperature and air speed that they felt comfortable with. There’s a couple of reasons for this. First off, the machines aren’t finely calibrated so there’s room for error in the hardware.

The second, and what is in my opinion the more important reason, is that everyone has a slightly different way of working. Heat and air speed are both subject to how far the iron is from the component. There’s going to be a “too close” and there’s going to be a “too far away” but there’s no perfect distance. I set my station to 380C and 60 air zoomies, Jessa set hers to 375C and 75 air, and Royce next to me had his set to 360 and 60 air. We all got the job done using roughly the same ballpark settings.

The most important lesson from this exercise was understanding how heat spreads through the work surface. We were working on a relatively tiny iPhone logic board with a relatively small thermal mass but heat management was still critical to get the job done.

If you’re working on an ATX mainboard and trying to remove the HDMI port and struggling with these settings, guess what? The thermal properties of your work surface require a change in tactics! The ATX board and the HDMI port itself are absorbing a massive amount of heat which means the heat you’re dumping onto the solder points is traveling away from the contacts and dissipating through the board.

So, what’d we learn today, class? A whole day of microsoldering school, and I didn’t even touch a soldering iron! But I got up close and personal with the technique for solving Touch Disease—which lots of people think even Apple wasn’t fixing, just replacing affected phones. It was also enlightening to get a feel for how heat behaves across the medium I’m working on. You could argue that soldering and microsoldering really boils down to understanding how heat behaves when it comes into contact with different materials.

With a few hours of microsoldering experience, I was already convinced that these techniques could save my time, my money, and my electronics. But what about other common problems on boards? Stay tuned for Day Two of microsoldering school where we’ll touch on: