PCB Forum - Recent Threads

RE: Logic Gate Output Changes When Nearby Relay Activates

DAB — Thu, 30 Apr 2026 20:54:14 GMT

Never underestimate the value of metal shielding.

Also, ferrite cores can be very useful in reducing induced spikes.

Logic Gate Output Changes When Nearby Relay Activates

eva_402 — Mon, 27 Apr 2026 08:08:51 GMT

Hi,
I’m using a few AND/OR logic gates to generate enable signals before they enter a microcontroller. The logic works normally, but sometimes outputs change briefly when a nearby relay switches.

The relay and logic ICs are on the same board.

Questions:

Is this more likely EMI coupling or supply disturbance?
Should I add more decoupling or flyback suppression first?
On the PCB, is physical separation between relay components and logic ICs usually enough?

RE: Logic Gate Output Changes When Nearby Relay Activates

colporteur — Tue, 28 Apr 2026 12:52:28 GMT

I've experienced the interference from relays in digital electronics. The components don't even have to be on the same board. Mostly working with Arduino's and raspberry pi. My fix was to code to simulate key bounce. relay contacts under heavy load do tend to generate emf. Its never seems to be good for the contacts and the surround environment. I can give you empathy but not a practical solution.

RE: Logic Gate Output Changes When Nearby Relay Activates

robogary — Mon, 27 Apr 2026 13:05:21 GMT

Depends. Is the relay switching an inductive load ?

If possible, you could remove the relay's load and cycle to see if that is related to misoperation.

Relay coils should have a flyback diode (or a shottkey double back diode tvs) unless it effects any critical timing. Larger coils should also have RC suppression.

If your relay switches an inductive load like a motor or solenoid, that load should also have suppression. The suppression will also ensure the relay contact life.

RE: Logic Gate Output Changes When Nearby Relay Activates

acdc90 — Mon, 27 Apr 2026 08:21:45 GMT

is the gates powered on 5volts

is the relays on 5v or 12v

does the relay have diode across coil

can we have a circuit ?

RE: Thermal profile methodology for DIY reflow — what I know, what I'm missing

BigG — Thu, 16 Apr 2026 16:53:00 GMT

An idea I had (needs effort to explore practical implications) is to place a layer of densely packed steel wool between the plate and the board to allow for warping and to provide a more even heat distribution. The thermal conductivity of steel wool will certainly be better than air but not as good as a solid metal plate.

Thermal profile methodology for DIY reflow — what I know, what I'm missing

pvit — Mon, 13 Apr 2026 00:22:40 GMT

Hi everyone. I built a compact reflow micro-table for hassle-free PCB assembly at home: [mention:8f821a5acb1c40a599317f20e3b6936a:f7d226abd59f475c9d224a79e3f0ec07]

I'd like to write a general guide on setting up thermal profiles, but I lack the practical experience to make something solid. I'm not talking about production-line requirements — more about "reasonably good" for advanced DIY.

What I know so far as hard constraints:

For RoHS/leaded: TAL no more than 60 seconds. For LTS — I'm not sure.
Ramp rate: 1–2°C/sec (except the start)
Cooling rate: ~4°C/sec; passive air cooling is acceptable (not sure about LTS).

Everything else seems to depend on the specific paste and equipment — recommendations vary widely. The bigger frustration is that datasheets give you a profile to follow but don't explain how much the parameters can actually vary. It's like the difference between a datasheet and a reference manual :)

A colleague with hands-on production experience described this simplified approach to me — I'd be curious whether it holds up in practice:

Ramp linearly at 1–2°C/sec
Wait until paste visibly melts across all components
Turn off immediately and let it cool

I'm keeping the scope to LTS and leaded — RoHS/SAC peak temperatures and tighter process windows are an unnecessary complication for beginners.

Questions

How important is a soaking plateau, and how does it depend on the paste type?
How long can components and the board stay above a given temperature before damage becomes a concern?
Is there a minimum time above liquidus required for proper intermetallic formation?
How critical is cooling rate — does the solidification speed affect joint quality, and what is generally preferable?
and so on...

I'd really appreciate input from people with real PCB assembly experience to help systematize the practical nuances — the goal is to put together beginner-friendly guidance on building reflow profiles from scratch.

I've also tried to document my limited experience with LTS pastes here: github.com/.../soldering_paste.md — feedback on what could be improved there would be much appreciated as well.

How to Position an SMT Stencil at Home

pvit — Wed, 15 Apr 2026 06:49:24 GMT

This is a positioning method that wasn't obvious to me until I'd tried a few other approaches. Sharing it in case it saves someone time.

The basic idea: use needles and fiducial holes to fix the stencil and PCB to a silicone mat. It's far more accurate and practical than building a makeshift frame with tape.

Use case

- Hobby use — assembling a few boards occasionally
- Open source projects where reproducibility matters (many people will build it)

What's out there

SMT stencil printers (full-size) — large, require dedicated space. Fine for production runs, overkill at home. Also needs a larger stencil, which drives up cost and shipping.
Compact stencil printers — appeared only recently. Much better suited for hobby use. Still somewhat large — might make sense for a dozen boards, but overkill for 1–2.
Fiducial hole positioning — has its nuances, but nearly ideal for hobby use. Unbeatable on price.

Hobby boards typically don't exceed 100×100 mm. In that case a steel stencil runs about $3. The question "solder by hand or use paste?" pretty much answers itself.

Worth noting: in "proper" stencil use the stencil doesn't touch the board — it snaps off during squeegee travel. With fiducial positioning the stencil lies directly on the board. In theory that's worse, but the results are good enough not to worry about.

How to do it

"Use needles and fiducial holes" sounds simple. In practice there are subtleties — needles come in different diameters, and repeatability matters.

For a long time I used AWG 22 steel wire with 0.7 mm holes:

Total offset no more than 0.1 mm
Sufficient for 0.5 mm pitch components

Downsides:

Still need to source the wire
Wire deforms when clipped, so zero clearance is impossible

On recent boards I tried something different. It turns out there are "location pins" at 1 mm diameter and smaller. At one well-known three-letter Chinese fab you can order them for pennies along with the boards. As shown in the photo, each location area has 4 holes — 0.6, 0.65, 1.0, and 1.05 mm — for 0.6 and 1.0 mm pins.

I went with 1.0 mm pins. Very happy with the results:

Pins drop straight into the board — no pushing into the mat
Zero play
Prints are even more precise. Multiple squeegee passes don't smear anything
Result does not depend on user experience

It's too early to call it 100% reproducible, but I've ordered boards this way three times with no issues. For extra safety you could add 1.05 mm holes next to the 1.0 mm ones, but I've never needed them.

If you know other convenient methods — share them.

RE: How to Position an SMT Stencil at Home

pvit — Wed, 15 Apr 2026 11:06:44 GMT

I just imagine squeegee path and keep pins aside. There are 4 corners. 2 pins required. Usually enough variants to select from.

From my experience, the only real problem is to position SMT stencil with ease and high precision. Everything else is not a big deal.

Also, dry paste (high viscosity) is a bit more convenient, but difference is not fatal.

RE: How to Position an SMT Stencil at Home

BigG — Wed, 15 Apr 2026 10:02:39 GMT

Good idea. I'm just wondering whether these pins will impinge on the solder application process. You typically apply solder paste on the stencil and then scrape across with a card etc.

RE: How to Position an SMT Stencil at Home

Andrew J — Wed, 15 Apr 2026 09:32:16 GMT

I just tape the PCB down to a board along as much of all 4 edges as possible so that it doesn’t move. With the stencil, I place a long piece of tape along one side. The stencil is positioned on the PCB so it is properly aligned then the stencil’s tape is pressed down onto the board (not PCB) and that allows the stencil to (a) not move whilst scraping paste across it; and (b) provides a hinge for lifting it off without disturbing paste. It also allows the stencil to be lowered back down if you’ve missed some paste or could do with more on some pads. Never had an issue with this approach.

RE: Thermal profile methodology for DIY reflow — what I know, what I'm missing

pvit — Mon, 13 Apr 2026 18:51:33 GMT

Yeah. Thin plate => bad heat distribution. Fat plate => slow cooling. I use Pi5 fan to blow from the bottom. It improves cooling speed 2x-3x until melting point reached. But that's still 1°C/sec. Something more serious will not fit device size.

The cheat is to end profile graph on melting point instead of room temp, lol :).

RE: Thermal profile methodology for DIY reflow — what I know, what I'm missing

wolfgangfriedrich — Mon, 13 Apr 2026 17:19:58 GMT

[quote userid="121623" url="~/products/pcbprototyping/f/forum/56848/thermal-profile-methodology-for-diy-reflow-what-i-know-what-i-m-missing/234961"]Using a hotplate like this is very much affected by the heat transfer between plate and board. It is necessary to press the board down on the hotplate since it will almost certainly warp as it heats up.[/quote]

This is probably the most important point to make a hot-plate work, at least when frying larger boards.

RE: Thermal profile methodology for DIY reflow — what I know, what I'm missing

wolfgangfriedrich — Mon, 13 Apr 2026 17:12:45 GMT

When I did have my DIY hot plate, I recorded some temperature profiles. With just turning of and convection cooling, the down ramp was never as steep a decline as the required profile. And the up-ramp was basically linear if there is not enough power or too much mass to heat.

(+) Arduino Hot Plate (2) - What's for dessert? - element14 Community

RE: Thermal profile methodology for DIY reflow — what I know, what I'm missing

pvit — Mon, 13 Apr 2026 14:36:44 GMT

In current configuration the ramp up is ~ 1°C/sec in high point. Cool down ~ 1°C/sec until go below TAL, then become slower and very slow at room temp.

RE: Thermal profile methodology for DIY reflow — what I know, what I'm missing

michaelkellett — Mon, 13 Apr 2026 09:06:37 GMT

For low volume home or prototype assembly I have found no value at all in setting profiles.

All the following is based on leaded solder - I have avoided lead free except for a few occasions using the CIF IR machine.

I currently mainly use a fairly expensive (CIF FT03 IR oven with internal air blowers) but before that I used under board hot air or a hot plate.

With the under board hot air (and a very cheap air blower) you have almost no control over the pcb temperature so the technique is to observe the solder paste and wait until it flows at all points on the board, then give a bit longer for luck. This process is not very repeatable 🙂 and I have known it to kill chips.

My hotplate technique used a cheap commercial hot plate. Set it to 30 - 50C above the solder melting point. Let it reach stability and place the board on it. Wait for the solder paste to flow - and then give it a bit longer.

Recently the CIF failed to flow a board with my usual profile because of the presence of a very large surface mount inductor.

The big SM Inductor and parts to the right of it and two of the SM capacitors did not solder in the IR oven using my standard reflow profile.

Rather than scrap the boards I used the hotplate on the corner of the board - considerable patience was required to reflow the inductor but the knowledge that the boards were scrap without soldering the inductor made me brave. The process worked and none of the other parts seem to have suffered.

Using a hotplate like this is very much affected by the heat transfer between plate and board. It is necessary to press the board down on the hotplate since it will almost certainly warp as it heats up.

The advantage of this process is that it can be used when you will only make (or salvage) one board and do not wish to scrap any. Developing a good profile requires experimentation. (My CIF machine could reflow the big inductor - I just wasn't willing to scrap a few boards to get there.)

Your colleagues advice seems mainly good to me if the hotplate can ramp fast with no overshoot - but my hotplate isn't very good at ramping quickly. I've never seen a hotplate that cools fast enough and I favour getting the temperature down by removing the board.

(Good solder paste and the use of a decent stencil are important !!)

Putting though holes of a decent size (1mm or more) in the big pads on the underside of chips allows you to check that the solder has flowed under the chip and may allow you to remove the chip if you have to.

RE: Thermal profile methodology for DIY reflow — what I know, what I'm missing

pvit — Mon, 13 Apr 2026 03:12:22 GMT

Personally, I have nothing against lead-free processes. But there are technical limits - existing power does not allow to reach desired ramp up speed for lead free. It's possible to reduce working area, but then comparison with MHP50 will be less impressive :). And as you noted, after additional temperature correction, to compensate losses, things may become too risky.

[quote userid="35177" url="~/products/pcbprototyping/f/forum/56848/thermal-profile-methodology-for-diy-reflow-what-i-know-what-i-m-missing/234958"]I would be interested in the temperature difference between your calculated temperature and the temperature on the top side of the board to be soldered[/quote]

According to cheap chinese thermal imager, and visual inspection of paste melting, in static state and 4-layer board with power polygons inside

about 10-15°C with LTS profile
about 20°C with leaded profile

And with notable delays on ramp up. As you can see on video, bottom right corner - one pin of buzzer is melted even after cooling phase started (probably it was located on corner screw hole). But this is very heavy scenario for "home use". Self-assembly is more acrobatics than normal use :)

Profiles are already adjusted - the leaded one has 230°C top instead 205°C. Probably, this can be more optimized, but this require more experience than I have in this area.

RE: Thermal profile methodology for DIY reflow — what I know, what I'm missing

wolfgangfriedrich — Mon, 13 Apr 2026 02:02:39 GMT

The colleague's method work well for me with an extra step to carefully push the soldered board off the plate after turning off. My plate has enough heat capacitance that the cool down rate is way too slow.

On your plate (very nice and clean design btw), I would be interested in the temperature difference between your calculated temperature and the temperature on the top side of the board to be soldered. My experience is that the top temp always lags a few degrees behind the plate temp itself. If you want/need to be profile correct, this difference matters and needs to be taken into account.

To your questions:

The soaking plateau gets more important the more copper you have in your board. A 2-layer board is very forgiving, but 4 or 6 layers are happier with the soak to get a more even temperature when ramping up into the liquid phase. Also prevents tombstoning.

Max temperature is mainly a concern of the FR4 material used, components are quite robust and have a little convection cooling working for them. The standard FR4 with Tg = 130degC of the cheapest offerings of your favourite Three-Letter board house works OK for one cycle of leaded solder profile. A lead-free profile with temperature up to 260 degC requires Tg of 170degC or better. The substrate gets brittle with compromised structural integrity.

Cooling rate is again a concern of tombstoning as a slower rate gets more uneven cooling. 5 or 6 degC/sec is preferred over slower rate.

And don't be afraid of lead-free solder process, it is no different when you use quality ingredients (as long as we are not talking low temperature solder).

RE: Protoboard Templates

colporteur — Thu, 09 Apr 2026 20:30:21 GMT

Your profile points count suggests you are new to the community. Welcome.

You will fit in well here, making an offering of your own work product. A Three-Way Prototyping Board for Awkward Through-Hole Components the link is for the ultimate perf board template.

The author of the board does some pretty amazing work. I've benefited a number of times when he has shared his work product.

Sean

Protoboard Templates

Tekkromancer — Thu, 09 Apr 2026 00:26:50 GMT

Hi all! I'm fairly new to electronics. To aid in my journey, I created some printable templates to help me plan out my circuits on protoboards on good old pencil and paper. So far, I just have two, but I'll certainly add more as I continue.

I'm happy to share them with the community in the hope that others will find them useful.

https://drive.google.com/file/d/1D_SknoozM5y2BAGld1N10K4CS7UIFK_e/view?usp=drive_link

Cheers!

RE: Protoboard Templates

DAB — Thu, 09 Apr 2026 20:28:36 GMT

Welcome to the community.

Feel free to as questions, we all learn something new everyday.

RE: Protoboard Templates

robogary — Thu, 09 Apr 2026 13:07:48 GMT

Welcome to E14 and the idea share.

Thats a great idea to avoid having to think and wire at the same time, get it right the first time.

In spite of years of practice, we all still make mistakes wiring prototypes and let the smoke out :-)

RE: Protoboard Templates

acdc90 — Thu, 09 Apr 2026 09:27:40 GMT

Hello hope you enjoy your time here and you will learn stuff,

The pattern you have drawn reminds me of the vero board i used to build A 8bit computer using wire wrap.

Do you have any projects in mind like interfacing to the real world

or do just want to learn about electronics

RE: LED_matrix_mosfet_driver_10x10

battlecoder — Thu, 26 Mar 2026 21:38:08 GMT

Nice. I love transistor-based project, so I like your approach.

Having said that, and echoing what @vmate already said; for this amount of LEDs it's normally desirable to have a higher level control interface with more features.
There's one controller I like a lot; the MAX7219 8x8 driver. It has a serial interface, so you don't need to worry about multiplexing or toggling LEDs individually, just feed the pixel data to the IC and will do the multiplexing for you. It also handles the LED current, which you can set externally, and it can also do BCD decoding if you use it to drive 7-segment displays instead of LEDs... And all of that with just 3 wires. Now, it's only 8x8, but it can be daisy chained to extend the display resolution without increasing the pin count.

There are advantages to directly addressable LED matrices like yours though, like the immediate response time of each LED, the fact that you can refresh the LEDs non-sequentially, and the ability to control them with analog or mixed logic, but I think those are slightly more niche applications so I expect that most people would probably be looking for something that frees the microcontroller from toggling the LEDs one by one.

LED_matrix_mosfet_driver_10x10

user_476 — Mon, 21 Jul 2025 06:43:48 GMT

idea for a mosfet driver to control a powerful 10 x 10 LED matrix or led strips, implemented with IRLML6344 and IRLML6402 transistors
LED_matrix_mosfet_driver_10x10

The project is basic, for development who wants to develop it.The idea was dictated by the fact that there is a missing of such drivers on the market
Here is a version with added resistors

LED_matrix_mosfet_driver_10x10._with_resistors