Chip Gets Real: Board Repair School, Part 2
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Chip Gets Real: Board Repair School, Part 2

This is the second of a three-part series about an iFixit writer’s week at a microsoldering and board repair class. Reading part one isn’t strictly necessary, but it will give you more insight into understanding how boards work, and the people involved in the class.

The middle of day three is when I truly wanted to quit board repair school.

After weeks of anticipation, driving three hours a day, and trying to power through a dense head cold, I was eager. Eager to wield hot lead, resurrect dead phones, and feel like someone people turned to in desperate need. I wanted to raise my eyes from my microscope, lift the phone out from underneath, and say something like, “Yep, just like I thought: this capacitor here had a short off the battery line, but I was able to patch it. Should be good as new.”

Instead, I had so far melted one phone’s display port with hot tweezers, mangled a chip replacement job, and demonstrated my clumsy multimeter technique in front of the whole class. I kept saying “open” to answer Jessa’s questions when I meant “short,” mixing up capacitors and filters, PP_BATT_VC and PP_VCC_MAIN. Learning how this stuff works was a brain-expanding thrill, but actually doing it made me felt like a dumb, clumsy human.

Jessa Jones, lead instructor of iPad Rehab’s practical board repair course, knew what was wrong with me, or at least with my approach. Her expert opinion: I needed a break.

“It’s very tiny s***. Moving it around is f***ing frustrating. You have to preserve the fun.”

Nobody, with enough practice and study, has failed to achieve competency in this field, Jones told us. Preserving the fun of board repair, Jones said, was the key differentiator between success and failure in the trade. You have to step back when you hit the wall, then come back to it like it’s a fresh problem. Besides that, it’s just diagnosis and practice.

That’s really what I learned in a week of board repair: it’s a trade like any other, people can learn to do it, and we could fix a lot more phones with it, if we cared enough to try.

The company that made your phone wants you to believe that any problem with its circuit board is irreversible damage to its soul, requiring a new purchase. And yet after one week, Jessa had nine people, some with little or no soldering or circuit board experience, finding and removing shorted components, replacing faulty chips, and wiring tiny jumpers by week’s end. This included me, after my hands lost their “beginner’s drift” and my brain had internalized some basic schematics.

Here’s how you get from “what is a diode” to having opinions about chip re-balling techniques in one week.

Hot Air and Fresh Chips

Workstation at iPad Rehab
My workstation at iPad Rehab, on the last day of class, as I disassembled a friend’s MacBook Air.

Each student in Jessa’s class gets a station, outfitted with Jessa’s preferred diagnostic and microsoldering tools. The big pieces are a microscope with a light and camera for a nearby monitor, DC power supply and voltmeter, Hakko soldering station, hot air station, and a mat. There are many little tweezers and knives, and expendable substances like flux and solder. Shared among all the stations is iPad Rehab’s vast supply of tools specific to their Apple-heavy work: jigs to hold specific boards in place, little digital things that test or connect through sockets and ports, and stencils for re-attaching tiny solder balls to the most common chips. 

Once we’ve learned what the parts on the board do, we take a closer look at the board itself. Looking under a microscope, we trace which parts run to ground versus connect to other components. We learn the difference between BGA and QFN chips. And we learn about two archvillains of board repair: underfilled chips, coated in a rubber substance that’s gruesome to pick apart, and important bits and bits that are closest to the CPU, where heat is most dangerous.

The bottom of the Meson touch chip I removed from an iPhone 6 board, in need of re-balling, and the chip laid next to the board it was removed from.

Before day one is over, we’ve got our first job. We’re going to remove, then replace, “Meson,” one of the chips with a connection underneath that tends to come loose and cause “touch disease.” We set our heat stations to 380 Celsius, soldering wands to 285 Celsius, and grasp tweezers specifically made to remove BGA chips. The job is to hook under the chip with the tweezers, then use that grip to lift the whole board. By applying the heat gun, the solder underneath should melt, and eventually the board will fall away, leaving the chip in our tweezers. This removal step goes pretty well, even if it takes me a long while to line up my hands with what I’m seeing under the microscope.

Backside of a chip removed from an iPhone board.
The Meson chip up-close, with some leftover solder balls waiting to be “deleted.”

Next, we need to “delete” the existing solder balls by wiping across the chip and its seat on the board with the iron. I stroke across the chip and its pad again and again, but I keep seeing gray, Hershey’s-Kiss-like spikes instead of flat, shiny pads. Mark, the other class instructor, says it’s simple: I’m not using enough flux. I try again and again, pressing harder, leaving the iron on for longer, adding more and more flux until I’m working inside a pool of diner-coffee-brown gel.

The real problem? Actually, most of the pads were fine, but looking at them from overhead, I couldn’t see that. You have to lift up parts occasionally and look from different angles, because at this eye-of-a-sewing-needle scale, you can’t always tell. Meanwhile, my whole station smells like scorched tree sap.

Presuming that my toasty chip still works, it’s time to “re-ball” it. This involves taping it to a stencil, pressing dry solder paste into the microscopic grid, then heating that paste with hot air until you’ve got 64 nice, shiny balls clinging to the chip. Except there are a bunch of tricks to how you tape the chip to the stencil, how you dry out and press in the paste, and how to keep the stencil from bending under your heat. Jessa and Mark each have their own preferences. Surely, I’ll remember and work through all this, though.

I fire up the hot air and wave it close to the stencil. The results are … crappy. Some balls flow over the top of their square, some are too tiny, and some look leaden and flat instead of shiny and round. Mark takes another look: I probably didn’t pre-heat the metal stencil properly, causing it to pull away from the chip. I also used too much solder paste. Mark is exceptionally patient and kind, but I’m glad he doesn’t congratulate me for not burning my fingers.

The way re-balling a chip is supposed to go, filmed at a different iPad Rehab class.

Class comes to a close before I can try it again. Some folks in class seem to have nailed the basics on their first try. Me, I’ve learned a lot, both about what holds devices together, and about patience and expectations. I drive home, rant to my wife about the day, fall asleep, shower, and drive back for day two.

Yeah, Well, You Should See the Other Guy’s Board

Most of day two is circuits and schematics. Toward the end, we switch on our soldering stations. We’re going to remove, and then replace, an input filter, or choke, next to the display port on our iPhone 6 boards. These chokes directly connect to one of the pins next to where you plug in the display, smoothing out the voltage heading there. If they fail, they are “open,” and power can’t get to the display at all all through that pin, no matter how many screens you replace.

My job is to drown the choke with flux, direct some heat at it, use hot tweezers to further heat up the pads at each of the choke’s four corners, then lift the whole thing up. This is less delicate work than the chip replacement the day before. My hope is that it’s just like heating up and pulling out a phone battery.

But I don’t have a good feel for where my tweezers are when I’m working on the choke. This wouldn’t be too much of a problem, if I wasn’t also (nervously) taking a long time to heat up and remove the coil. My too-close-to-the-board tweezers mutilate a significant part of the display port itself, joining together some pins and outright obliterating a few others.

Annotated image detailing board damage during a choke replacement
Insightful post-mortem I sent to my iFixit colleagues after my first attempt at a filter replacement.

But there’s enough time to take a second shot at pulling an input choke near a different port. I once again get too close to the port, but this time I don’t actually damage the connectors, just heat them up until they’re silver. I show Jessa my work. Her advice: take the win and move on. Also: next time, put Kapton Tape on the port.

Annotated image detailing a replaced choke on an iPhone board
It’s the (very) little things that keep you coming back.

A Wire in Uncertain Times

I stay over at a friend’s house in Rochester the night before day three. My cold gets worse, the heat is cranked much hotter than I’m used to. And the Walgreens nearby doesn’t open until 12 minutes after I get to it. Sitting in my car, sneezing and shivering, I start thinking about whether I’ve oversold this experiment to my boss, to myself, to anyone reading this. I’m messing around with concepts beyond my grasp, and seemingly blowtorching every iPhone board I touch. I’m not even going to be fixing phones after this. What’s the point of this, exactly?

We witness a phone-resuscitation miracle that morning. It’s a real Road to Damascus moment in my education on what you can do with heat and schematics. Still, I’m not too excited about our practical exercise that afternoon: running a copper wire, of human hair thickness, as a jumper between a chip pad and a nearby component. How many wires will I blow away, or stick to each other, before I’m done?

This is a little bit different than pulling board bits for practice—it’s practical, a real thing board repair techs do. Some chips, placed right in the bendiest part of a logic board, can have some of those tiny solder balls crack or come loose underneath, severing the connection and causing things like the no-speaker “Audio IC” issue on the iPhone 7. Running jumper wires like this ensures that after replacing the popped-loose chip, further bending won’t cause the problem to re-occur.

I pick up my frenemy, the iPhone 6 board, and navigate to the empty spot I left after failing to replace the chip on day one. I grab a pair of tiny-tipped tweezers, pinch of a length of tiny wire, and burn the insulation off of it. I lay down a river of flux near the pad, put a small amount of solder on my iron tip (wiping most of it off on the brass wool), then navigate the wire over toward the chip pad. I’m halfway through bending the wire toward the other component when I realize: I’m doing this.

A microscopic wire jumper run from a chip pad to a component
A thin wire, soldered between a chip pad and a nearby component for practice (the author would clean up those pads before re-adhering a chip, he swears).

I was so focused on how bad I was going to be, I didn’t notice that my hands and eyes had a better sense of depth under the microscope. Or that I’d lost a lot of my “beginner’s drift” when applying my iron. I had a steadier hand; when solder from a nearby pad jumped over to my pad, I calmly twisted the tip a bit and let it shrink back to its spot. 

Mark comes over, checks my wire, and declares it legit. “If you can do that, there’s not a lot you can’t learn to do.” I do a couple more jumpers for practice. I’m developing a mental sense of what everything feels like, and how it all responds to pressure: board solder, lead solder, capacitors, wires, pads. I don’t have to spend two or three minutes just finding my spot under the microscope anymore.

As weird as it seems, this is the kind of fun you have to preserve. 

Fixing the Pixel 2 I Killed

By day four, we’ve somehow fixed most of the students’ seemingly dead iPhones. Jessa asks to see the Pixel 2 I brought in. It was one of my best friends’ phones; the screen stopped working after I replaced the battery. I had bought a new screen, but it showed a severely dim, off-color image. I brought it to a repair shop after that, and they had the same experience with yet another genuine replacement screen. It made no sense, to me or anyone I ran it by; I had all but given up on it.

There are no schematics for the Pixel 2 floating around, nor a market of board-level parts. But just letting Mark and Jessa look at it for 10 seconds under their microscopes, they both said they knew the problem. They would let the class look and see if they could spot it. Now let’s see if you can.

Close-up view of the corner of a Pixel 2's display port
The no-display Pixel 2’s display port and nearby bits.

Every component near the port looks a little different, there’s seemingly some corrosion around one of the port pins, solder balls with nothing on them (known as “no-stuffs,” or board sections intentionally left without components on some models). And one of the capacitors looks a little golden-brown rusty. But the real issue is what’s not there: two filters (upper-right-most in the image above), whose empty pads, along with the dark board coloring, trick most students’ eyes into missing them.

We’ve talked about “prior technician damage” a lot in this class, as something to look for when examining a board. In this case, I am the prior technician. I am the damage. I pried those filters up, when I used too much force in removing the display connector. Looking at the components, Mark guesses that one of them is a capacitor that can be left off, but the other is a filter that has left a line open between the display and the board. We’re short on time for the day, so Mark does the wire-jumping himself.

Running a jumper wire between the pads of a disconnected filter on a Pixel 2 display port
Soldering a wire between the pads of one missing filter. Grains of medium-length rice added for scale.

Mark hands me the phone, and I walk over to the charging table. I grab the replacement OLED screen, snap it in place with my finger, plug in the charging cable, and … the Google logo appears, in all its primary-color glory. Less than a minute later, the lockscreen appears, and responds to touch. It took Mark a minute of examination and 5 minutes of work to save the phone that nobody could figure out.

Post-surgery Pixel 2.

This is the point. This is why I came here.

Your author, removing a Tristar chip from a board with heat, tweezers, and much steadier hands on day four of class (Sorry for the bad microscope arm and heat gun angles).

Next week, I’ll wrap up my experience at board repair school talking about the economics, politics, and business of board repair. I know how that reads, but I promise: I will keep it fun.