Applying solder paste to a new custom PCB is always a little nerve-racking. One slip of the hand, and you have a smeared mess to clean up. To make this task a little easier, [Max Scheffler] built the Stencil Fix Portable, a compact self-contained vacuum table to hold your stencil firmly in place and pop it off cleanly every time.
The Stencil Fix V1 used a shop vac for suction, just like another stencil holder we’ve seen. The vacuum can take up precious space, makes the jig a little tricky to move, and bumping the hose can lead to the dreaded smear and colorful language. To get around this [Max] added a brushless drone motor with a 3D printed impeller, with a LiPo battery for power. The speed controller gets its PWM signal from a little RP2040 dev board connected to a potentiometer. [Max] could have used a servo tester, but he found the motor could be a little too responsive and would move the entire unit due to inertia from the impeller. The RP2040 allowed him to add a low pass filter to eliminate the issue. The adjustable speed also means the suction force can be reduced a little for easy alignment of the stencil before locking it down completely.
We love seeing tool projects like these that make future projects a little easier. Fortunately, [Max] made the designs available so you can build your own.
Typical overengineering! Using RP2040 (dual core MCU, 133 MHz, 262 KB RAM) to make a… low pass filter? Can be done with just one resistor and one cap (6 dB low pass filter).
Read again. He is controlling the speed controller too.
“The speed controller gets its PWM signal from a little RP2040 dev board connected to a potentiometer.”
You could have put a low pass filter on the pot itself for the servo tester.
If the potentiometer is part of the oscillator loop (like in a basic 555 circuit), it’s not easy to lowpass it.
If you want to be pedantic you can pretty easily make a PID controller to generate PWM signals using some opamps and 555 timers. As all good hackaday comments should point out.
You won! We’re going to make you King or queen of the winter carnival.
Getting to ride on the float is important!
Typical troll comment, never occurred to you that they used the parts they had on hand and wanted to use. It’s their hobby, you don’t get a say in the “right” way for them to have fun or spend their time or money. If you wanted it done differently then get away from the keyboard, make one yourself and post about it online.
Beginner: Learns the one most popular high-power microcontroller of the day and uses it for everything. We’ve seen this with Basic Stamp, Arduino, ESP32, Pi-Pico… etc…
Graduate: Realizes they don’t need that power for a simple project, finds the perfect MSP430 or maybe even 555.
Professional: Is building widgets w/ Microcontroller X all day long. So what if it’s overpowered.. why learn a whole new environment just to save 1/2¢ on a one-off? That makes no sense!
Know it all: Complains about what someone else used. Builds nothing.
Professional designing real products:
– Don´t use a microcontroller if you can easily avoid it.
– Find failure modes and improve robustness
– Then cost.optimise without loosing robustness
Where did you learn that? I thought it’s the opposite… BOM cost > everything.
That really depends on which industry you are. The hugh volume consumer products are more sensitive to BOM cost, but for some small quantity products, a reliable solution and ready to use code base and/or tool kits is more important.
Defense contractor: uses FPGA.
Masochist: insists on using the cheapest chip possible and tears their hair out with optimisations to make it work
Exactly – who gives a sh.. if the chip is over-powered, it’s a few bucks and they’re everywhere, why would you bother even looking around unless you were planning to make a million of them?
+1
It’s the right choice for a one-off prototype type device. Allows you to add things later, maybe an LED to indicate something, a servo to open close a valve, timer for auto shutoff, temperature sensor…
You got that micro and maybe some python (I’m kinda appalled myself here) and this can be knocked out in minutes rather than hours.
Not everything has to be optimal in terms of cost and resource usage.
How much does a rp2040 board cost? Very little so it is hardly a waste to use one that you already have in a one off project.
It is also likely much faster to do, rather than trying to figure out if you can add a low pass filter to the servo tester which might not be the case.
RP2040 costs 1$, so it really is a reasonable solution to replace e.g a bunch of 7400 series TTLs, or a 555, or even an analog passive filter. To think otherwise is like complaining that a steel hammer is overengineered because it requires the services of a coal mine, coke factory, steel mill and a foundry, whereas a rock would do the job.
Considering the article says they started with a simple and cheap off the shelf servo tester, that probably is about as basic and ‘passive’ (though likely a globtop) as it could possibly be to do the job, and found it wasn’t good enough the next logical step is go for something like the Pico – its a prototype you have just learned is too sensitive to how the motor is spun up etc, so you want something you can alter a variable in the code till you get a good result and thus know what actually matters.
Now once you know the interactions between HID parts and machine that works nicely for the motor speed control you could go for lots of more passive components to get the job done, but there almost is no chance that ends up cheaper than a RP2040 for small runs anyway.
I thought I understood how SMD stencils work, that’s until I saw that eyeballing some liberal amounts of solder paste, straight from a syringe onto the pads, also produces good results. Is it necessary for a short run in the home lab?
Really depends on what packages you are soldering. For most larger soic smd parts pasting manually is good enough with some potential small touch up with an iron afterwards, for tight pitch stuff with no easy way to get an iron in there like qfn or worse bga then a stencil is probably worth the investment and effort.
I had a go at using solder paste for the first time today: on a 2x2mm LGA-12 accelerometer. I’m glad I had room for tweezers around the chip, as it took three or four attempts to get a reasonable join on all pads. (Main learning point: be more generous with the paste in the first place.)
Paste was applied by the high-tech method of using the end of a toothpick. I didn’t have a solder stencil made, as it would have cost nearly the same as the small batch of PCBs I’d ordered.
Using a syringe and needle works well too, just make sure you get something to help squeeze the syringe.
Our Chinese friends sell small squeeze bottles with an assortment of dispensing tips for henna tattoos. They are much easier to work with than syringes.
So the stencil alignment is just eyeballed? Seems like a missed opportunity to stick a couple of alignment pins in the stencil part.
Neat idea though, especially for hobby stuff.
This. Alignment is critical, detaching stencil in a controlled way is even more critical.
Wrong side of the project was overengineered.
I’d have to disagree a little – as registration and the like is going to be different for different PCB anyway. The same tools that built this tool can create the right registration jigs to go with it for every board you want to work on, so unless you always work with some standardised features to make a single alignment jig sufficiently universal I don’t think you can mark this down for that.
Discovered this a while back. A controlled way to dispense solder paste with a syringe. Haven’t tried it but it looks promising:
https://avdweb.nl/tech-tips/pcb/solder-paste-dispenser
And then there is the Pixel Pump to assist with P&P by hand:
https://www.crowdsupply.com/robins-tools/pixel-pump