AliExpress is a great resource for finding affordable components, but you have to be careful about the quality of what you actually receive.
I just released a new video that covers nine components I'd never let anywhere near a product I'm building.
One of them gets sold as a humidity sensor when there's no humidity sensor inside it.
Another one is a fire risk with a label claiming triple the capacity physics allows.
The worst part is that a counterfeit component almost never fails on the day you solder it down.
It fails once your product is in a customer's hands, and at that point you're paying for a whole production run over a two dollar part.
And you're already debugging your own design, so the last thing you need is to be debugging your parts at the same time.
Now, if you're building a hobby project or a one off for your bench, buy whatever you want, because a bad part just means ordering another one.
But a product headed for production gets held to a different standard, since that part gets multiplied by every unit you build, and it has to be the same part when you reorder next year.
Fake components fail in three ways: they don't work at all, they work worse than the label says, or they work right up until they don't.
So let's count down nine of the worst offending AliExpress components, ending with one that actually endangers your customer, and for every single one I'll tell you what to use instead.
Component #9 - FTDI USB to Serial Chips and Cables
The FT232 from FTDI is probably the most counterfeited chip in hobby electronics, and the fakes are convincing enough that your computer can't tell the difference.
Back in 2014, FTDI pushed out a Windows driver update that detected the clones and reprogrammed their ID number to zero, which left them permanently dead.
A later version stopped killing them and instead made them send the text "non genuine device found" out the serial port, which corrupted the data going to whatever was listening.
Now picture that being your product on a customer's desk, and it stops talking to their computer after a routine Windows update they didn't even choose to install.
You changed nothing, but you're the one taking the support call and paying the return shipping.
So if you need a USB to serial bridge, buy the FT232 from an authorized distributor like Digi-Key or Mouser, so you know you're getting an authorized FTDI part.
And if cost is what's pushing you toward the cheap option, the CH340 from WCH and the CP2102 from Silicon Labs are both perfectly good parts when you buy them through legitimate channels.
Component #8 - Sensor Modules
The BME280 breakout board is the poster child for this one.
The BME280 from Bosch measures temperature, pressure, and humidity, while the cheaper BMP280 measures temperature and pressure with no humidity sensor at all.
Plenty of listings sell BMP280 modules with BME280 printed in the title, and the two boards look identical.
You wire it up, run a standard BME280 library, and it refuses to start, because that library checks the chip's ID and gets the wrong number back.
Then you go hunting through your wiring, your pull-up resistors, and your I2C address, when the real problem is that the chip isn't the one you ordered.
The good news is that same ID register tells you exactly what you're holding.
Read it, and a real BME comes back as hex 60, while the humidity free BMP reads hex 58.
For anything going into a product, buy the module through an authorized channel, or better yet put the sensor on your own board where you control the sourcing.
Component #7 - STM32 Microcontrollers
The STM32F103 is one of the most cloned microcontrollers on the planet, and what shows up on a lot of those cheap boards didn't come from ST at all.
Sometimes it's a pin compatible part from another manufacturer with ST's markings reprinted on top, and sometimes it's a lower grade part remarked as a higher grade one.
Those chips almost always boot, they run your blinking LED demo just fine, and then they drift from the datasheet in small ways.
That means timer behavior that's a little off, a peripheral that doesn't do what the reference manual says, or a flash size that doesn't match what the part number claims.
You end up tearing apart your firmware for weeks when your firmware was never the problem.
There's a second issue that matters even more for a product, since you can't reorder these with any confidence when the next batch could easily be a different die.
Buy your microcontrollers from an authorized distributor like Digi-Key, Mouser, or Arrow, which covers you from prototypes all the way through your early production runs.
And once your volumes climb into the tens of thousands, ask your distributor for a volume quote or go talk to ST directly, because nobody in production keeps paying catalog price.
Component #6 - Name Brand Electrolytic Capacitors
When you see Panasonic, Vishay, or other premium brand capacitors selling for a fraction of the distributor price, what you're actually buying is a plastic shell with a respected brand name printed on it.
That shell is the easiest thing in the world to fake, and what's underneath it is usually a low grade cap with the wrong ESR and a much shorter life.
ESR stands for equivalent series resistance, which is the internal resistance of the capacitor, and it affects how well that cap responds to sudden changes in current.
More importantly, ESR controls how much ripple current the cap can handle before it heats up and dries out, which makes it a reliability problem rather than just a performance one.
Get that wrong in a switching power supply and your product doesn't fail on your bench, it fails eight months later across your production run.
We already saw how bad this can get with the capacitor plague back in the early 2000s, when bad electrolyte took out motherboards by the millions.
So buy your electrolytics from authorized distributors, and if your budget is tight, remember that a quality cap from a budget brand will always beat a fake version of a premium brand.
Component #5 - Power MOSFETs
A MOSFET is just an electronic switch, and the whole reason you pick one specific part is the numbers on its datasheet, meaning how much current it carries, how much voltage it blocks, and how hot it gets doing both.
Counterfeit power MOSFETs are typically a smaller, cheaper die inside the right looking package with the right part number etched on top.
It'll pass a bench test at low current every time, and it may even handle your full rated current at room temperature.
Then you run it inside a sealed enclosure on a hot day, that undersized die can't shed the heat, and it fails.
Even when it survives, running a small die past what it was built for damages it a little at a time, so the part dies months later in the field instead of on your bench.
This one bites hardest in motor drivers, battery chargers, and anything else switching real power.
Power parts are the last place to save fifty cents, so buy them from authorized distributors, full stop.
And if you inherit a design with mystery FETs already in it, load test one at its rated current under worst-case conditions before you trust it across a production run.
Component #4 - Lithium Charging and Protection Boards
Those little charging modules built around the TP4056 from NanJing Top Power are everywhere, they cost about fifty cents, and they're handy to have on a bench.
The trouble is what's actually on them.
The charger chip is often a clone, the charge current gets set by a single resistor the seller picked with no idea what battery you're using, and the protection circuit is sometimes missing entirely, with bare pads where the protection chip and the two switches that cut off the battery belong.
That means you can end up pushing 1A into a 400 mAh cell because the board came configured for a much larger battery, with nothing watching for an over discharge or a short.
That's a lithium cell running with no safety net inside a product you're shipping to your customers.
For a real product, put the charger chip on your own board where you set the charge current for your specific cell.
Parts like the MCP73831 from Microchip, or my favorite, the BQ series from TI, are cheap, well documented, and they let you verify exactly what you've got.
Component #3 - High Capacity 18650 Cells
You'll see listings for 9,900 mAh 18650 cells, sometimes even 12,000 mAh, for a couple of bucks each.
Physics doesn't allow that, since the best cells Samsung, LG, and Panasonic can build in that can size top out around 3,500 mAh.
So anything claiming way more than that is a rewrapped cell, often a used pull from a scrapped laptop pack, and the measured capacity is frequently under 1,000 mAh.
The fake capacity is the smaller problem here, because you also have no idea what that cell has been through, what its internal resistance looks like now, or whether it has any protection circuitry at all.
Putting a cell like that inside a product you're selling means you're knowingly carrying a fire risk, and the recall and liability that follow are yours alone.
Buy your cells from vetted distributors who can trace them back to the actual manufacturer, and capacity test every cell before it goes into a build.
Component #2 - Fuses and Safety Rated Capacitors
Fuses and safety capacitors have one job, which is to fail correctly when something else goes wrong.
A fuse is supposed to open at a specific current within a specific amount of time, so it cuts power before anything else overheats.
Safety rated capacitors are the X and Y capacitors sitting right at your mains input to filter out electrical noise, which puts them in the most dangerous spot on the board.
An X capacitor goes across the two mains lines, a Y capacitor connects a mains line to ground or to something your customer can touch, and both are built to fail open rather than short out.
Counterfeit versions of both are everywhere, and the safety agency marks printed on them are just ink.
A fake fuse that holds at three times its rating is a disaster waiting to happen.
And a fake Y capacitor that shorts instead of opening puts mains voltage somewhere a person can touch.
There's no bench test that rescues you either, since a safety part only proves itself during the one event you hope never happens.
This is the one category where I wouldn't even weigh the tradeoff, so buy safety parts from authorized distributors, verify the marks are real, and keep the paperwork.
Component #1 - Mains Powered USB Chargers and Power Supplies
These are the two dollar wall adapters that plug straight into an outlet, and teardowns of the cheap ones turn up the same problems over and over.
The isolation barrier between the mains side and the low voltage side measures under 1 mm in some of them, when safety standards call for several mm of clearance.
The certification marks molded into the case were never earned by anybody, and basic input protection like a fuse or a surge suppressor gets left off to save a few cents.
Buying one of these for your own bench is your call, but designing your product around one is where I'd draw a hard line.
If that supply fails, dangerous AC voltage may make it to the low voltage side, and that puts your customer at real risk.
So use a certified supply from a real brand that will hand you an actual test report with a certificate number you can look up yourself.
Talk soon,
John
P.S. If you need help with component selection and sourcing for your product, then you can get help from me and other experts inside the Hardware Academy.