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• PCB ready

  Vitaly • 06/19/2020 at 07:52 • 0 comments

  Finally, assembled couple of PCBs:

  Now can debug drivers and print case.

  I'm still thinking about USB-PD version. It should contain less components and be more compact. Anyway, software architecture is flexible enough to support both. We will continue with current PCB to test usability, and will order USB-PD version in parallel.
  

• PCB & Case

  Vitaly • 02/19/2020 at 03:23 • 0 comments

  Finished drawing PCB & case:

  All links & sources are on github: https://github.com/puzrin/reflow_micro.

  Now plan to spend several days for additional checks. Then will order components and try to print something working until electronic parts arrive.

• Final heater tests with 2/3/4mm plates

  Vitaly • 02/12/2020 at 22:56 • 0 comments

  Made more heaters with plates of different thikness, to test temperature difference. Thermal camera shows only general picture, so used K-thermocouple via drop of rose metal to check most hot (~ center) and most cold (corner at wires side) points. Checks have been done at medium (~ soaking) and high (~ peak) temperatures.

  4mm:

  • medium: 176-181°C, Δ = 6°
  • high: 263-271°C, Δ = 8°

  3mm:

  • medium: 184-191°C, Δ = 7°
  • high: 272-282°C, Δ = 10°

  2mm:

  • medium: 163-170°C, Δ = 7°
  • high: 269-282°C, Δ = 13°

  As conclusion - 4mm plate is good for any cases. It still can be cooled fast enough with fan.

  Pictures of winner:

  What's next

  PCB is already complete: https://easyeda.com/reflow/reflow-micro-table. But i'd like to draw device case and verify PCB outline and other things.
  

• New MCH mounting (close to final)

  Vitaly • 02/02/2020 at 22:26 • 0 comments

  Finally tested a lot of ideas & new method of MCH mounting:

  • Pre-assembled aluminium heater cartridge (not MCH).
  • MCH mounted on copper plate (70*60*2mm).
  • MCH mounted on aluminium plate (70*60*2mm).

  Here is "almost final" candidate:

  Bottom:

  All assembly details and more photos are published on gihtub (will be updated soon): https://github.com/puzrin/reflow_micro/blob/master/doc/heater_assembly.md

  Key points

  1. M1.6 stainless steel screws are enough for good thermal insulation. PCB stays cold.
  2. New plate has 60*50...70*60 mm of working area with acceptable temperature difference. That's ok for 99.9% of hobby projects.
  3. ~40-50W needed to heat plate of this size to 270C.
  4. Sizes & technology confirmed, can start PCB trace.

  Rejected attempts

  Not everything was fine. Unfortunately, rejected aluminium heater cartridges:

  1. They have not enough power to reach desired temperature (announced 300W are for cold state, at 220-230C power drop to 30W).
  2. Power wire are fat and become too hot - difficult to place in compact device.
  3. No 110v versions (for USA)

  Also, i had to reject copper plates in favour of aluminium. Copper is oxidised too fast on high temp. I hoped oxidised film to stop process, but it crumbles after big temperature change. Probably, this can be fixed by protecting plates with paint from all sides, but that's not convenient.

  40*40*1.7mm MCH heaters were tested, but found 50*50*2mm more comfortable. Price difference is very small.
  

  What's next

  As been said, new approach looks good at first glance, and now it's safe to route PCB and design 3d-printed case. All next experiments can be done in parallel.
  

  It still worth to clarify plate thickness. 2mm aluminium plate  gives ~ 15C difference in working area (5mm margin from borders). That's enough, with big reserve, for leaded paste (i doubt anyone use lead-less paste for hobby projects). But it would be nice to improve if possible.

  I'm waiting 3mm and 4mm alu sheets for new plates and hope to publish final decision & measurements next week.
  

• MCH temperature measurement and other thoughts

  Vitaly • 11/28/2019 at 00:28 • 0 comments

  While thinking about device layout, remembered interesting idea about temperature measurement. MCH heaters use wolfram film routes inside ceramic. Wolfram has big TCR, about 60% per 100C. So, we can use heater's resistance to measure temperature precise enough, without any additional sensor. The same method is used in vape mods with temperature control.
  

  If no need to mount sensor, that extends the list of available components. Try to search "LED Remover Heating Plate" on AliExpress. You will see nice interesting plates like this one. I don't know how good are those (temperature gradient and cooling speed), but worth to try. Unfortunately, those alu-coated plates are 220/110 volts only.
  

  I need to decide, does it worth continue with USB-PD, or switch back to AC. Bellow are summary of differences.

  Differences between USB-PD and AC powered micro table approaches

  USB-PD powered:

  • Safe.
  • Compact.
  • Can be done without case at all.
  • More difficult to develop
  • More easy to use touch screen

  AC powered (with alu-coated MCH):

  • Small size possible only without galvanic isolation, power switch, and with AC cable directly wired to PCB (without connector).
  • 3D-printed case become mandatory for safe use.
  • May be, more big size of useable surface (not tested yet)
  • May be, more easy mounting (without aluminium foil and SS wire)
  • No touch screen. Ordinary display + encoder.
  • More easy to finish development

  For AC, resistance control can be done with "energy meter" chips (BL0937, HLW8012).

  What's next

  I've ordered "aluminium heater", referred above, and wish to test it before moving forward. Hope this to happen in 2-3 weeks.
  

  Let me know what do you think. I'm sorry, if USP-PD is critical for someone. But i hope any planned changes will do project better - still very small, but more simple,  and so on.
  
  

• MCH mount. Episode 3

  Vitaly • 11/20/2019 at 17:36 • 0 comments

  Finally achieved very good results: MCH top 260C, bottom mount points 45C (screw heads), PCB almost cold. Only 10mm space between PCB and MCH. That's a win :). See photos and read details below.

  Details

  Idea is very simple - take 2 thin SS screws, sharpen ends and mount to PCB with 2 nuts from both sides.

  Screw sharpening can be done with screwdriver and hand grinder:

  • Place 2 nuts on screw, one at cup, another more close to the end.
  • Put this into screwdriver (use nuts to hold).
  • Rotate screwdriver left, and sharpen screw end with grinder.

  If your screwdriver has axial oscillations, cone will be not symmetric, but that's not principal.

  What is important:

  • Screw should be stainless steel, not carbon steel. SS has lower thermal conductivity.
  • Screw dia should be M2 or less. M3 has twice less section than M3 - lower thermal conductivity.
  • PCB reflector should use ordinary aluminium adhesive tape. DON'T use reinforced tapes for auto tuning, those have not enough good IR reflection and heat distribution.

  After all, assembled device can work many hours (was tested!), and keep PCB slightly warm. The most hot points are screw heads, and those are only 45C.

  What's next

  Finally, i have working solution to move forward:

  • Easy to repeat.
  • Safe enough to place electronics on the same PCB.

  But in real device I plan to use M1.6 screws (almost twice less section than M2) and check additional things:

  • Can we use screws "as is", without sharpening (assembly simplification)?
  • Can we reduce interval between PCB and MCH even more (device size)?

  Now, time to route PCB :). All details will be at https://easyeda.com/reflow/reflow-micro-table.
  

• MCH mount. Episode 2

  Vitaly • 11/04/2019 at 15:46 • 0 comments

  Finally, after waiting for new materials, checked some ideas and here are new details about MCH mounting.

  New heroes :)

  Left is with:

  • black paint on top
  • aluminium foil on bottom
  • thermal reflective adhesive tape on PCB

  Right is with:

  • Panasonic PGS + black paint on top
  • aluminium foil on bottom
  • thermal reflective adhesive tape on PCB

  Don't pay attetntion to dirty surfaces, that's after testing coverage quality.

  Heater bottom side barrier

  I wished to find better replacement for high temp silver paint. Classic solution to reduce IR emission is aluminium foil. So, needed to find suitable foil thickness (convenient to work with) and suitable glue (good at 300-400C).

  First, any foil is ok to reduce (or reflect) IR emission. But too thick foil may be not convenient for mount. After search, i found nice foil in disposable aluminium baking forms :). It's ~ 60um thick (kitchen foil is 10-20um), cheap and easy to buy. The only advice i can give - select form with flat bottom.
  

  Glue is a different story. There are only 2 types of accessible glues for desired temperature range:

  • RTV-1 silicones. Gasket makers for auto can work up to 350-370C.
  • Silica cements (exaust systems repair glue, for example).

  Problem is, we need thick layer, and this glues dry not well without air. Also, cement is not convenient for work.

  Since foil on MCH bottom does not need full surface bonding, we can use gasket maker. If we put small glue points on corners and between, that will be enough to hold foil well. And glue will dry completely in 1-2 days.

  I selected copper-filled gasket maker, to use it again later as thermally conductive glue for RTD sensor.

  How to bond:

  • Put small glue points on corners and between.
  • Cut foil peace with margin, place over and press with flat surface.
  • Wait ~4 hours until silicone dries good enougth.
  • Cut foil with sharp knife by heater perimeter.
  • Need to wait 1-2 days more for full dry, but from this moment we can start paint heater top with black paint.

  Heater top side cover

  I had idea to use Panasonic PGS to equalize surface temperature. But, to be honest, amount of problems are not proportional to added value.

  • Only pure PGS (without protection & adhesive layers) can operate at 400C.
  • Cements do not hold PGS at all
  • RTV-1 silicones can hold PGS but don't dry well at 50*50mm area in thin layer.
  • PGS is very soft, and needs protection layer. Can be parcovered with paint, but that will not live too long.

  Of cause, there are 2-component epoxies and thermally-cured 1-component glues, able to work at 300+ C. But those are not cheap, and not widely available.

  Here are 2 thermal images, as a result of experiments. Don't be too critical to temperature values - i used different paints and did not tuned camera.

  Ordinary black top:

  
  Top with PGS (poorly bonded with copper-filled silicone gasket maker):

  So, may be, PGS can help a bit, but it's not "magical" for this appliance.

  My opinion is - use any black paint, able to work at 400C and more. Usually, all such paints have good adhesion to ceramic. So, select the cheapest one. Take care to manial, usually after dry, heating at 180C (or more) required for 1-2 hours. Since we paint heater - that's not a problem at all. 
  

  Useable heater area

  As you can see on thermal images, ~15-20mm from power wires are not heated well. The rest is ok, if we do some discount for hobby use:

  • Nobody uses lead-less paste for hobby.
  • Even with 30C surface difference we have enough reserve if lead-less paste used (melt at ~180C).

  I'd say, there will be ~30*45mm of "solderable space". Very nice.
  

  Is it possible to do something better? Yes, of cause. But advantage of this device is to be small and easy to do, good for rare use. Such simplicity compensates it's disadvantages for many cases. If you need something better - use microwave ovens, bga reball stations and so on. Segment of bigger devices is already well-covered.

  PCB reflective layer & mounting

  PCB cover is not principal, because almost everything is already dimmed by heater's foil. Use any reflective adhesive tape,...

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• Experiments with MCH mount

  Vitaly • 10/19/2019 at 04:35 • 0 comments

  Since i need to make "popular" project, i use only accessible materials. Those may be not ideal, but that's intended choice.

  Don't be confused with photos, those use special test boards for MCH only. With electronics and safety margins size should be ~ 130*70mm.
  

  Attempt 1. Classic insulation.

  I started with standard approach - putting insulation between heater and PCB. Found some kind of "aerohel" on aliexpress (not pure), and tried it:

  Result was not impressive:

  • Bad insulation
  • Too slow cooldown
  • Too many dust (not dangerous, but dirty => unpleasant)

  For sure, tried 3 layers of 6mm material with aluminium foil between. Better, but not enough. And with too slow cooldown after power off.

  So - don't try to repeat, that's a road to nowhere :)

  Attempt 2. Air gap + reflectors

  After failed first attempt, i changed approach to air gap + IR reflector.

  I did "spot mount" heater on conic bolts and placed acrylic mirror sheet on PCB.

  Result become much better, but still needed some improvement. As i found later, my main mistake was to use acrylic mirror in reflector. Probably, aliens stolen my brain when i puchaised those while having normal aluminium adhesive tape.

  Let's skip this step and follow to improved attempt, with more details

  Attempt 2.1, air gap + right reflector

  Here is our hero:
  

  Let me list all condition for best result:

  • Maximize heater IR emission up
  • Minimize heater IR emission down
  • Minimize direct contact between heater and mounting to PCB
  • Reflect IR waves from PCB

  First, i prepared MCH heater: painted top with black temp resistive paint, and bottom with silver paint. Also used second heater with black-top-only, and third unpainted heater to compare. As real hobbist, i powered all 3 heaters, and used hand to feel heat on 1-2cm distance :). Difference was VERY big.
  

  Many of you know, heater must have black top for better work. I can add - it must have reflective bottom to reduce losses and simplify insulation. I'm not sure silver paint is ideal, but have some ideas how to improve.

  Now let's see mounting. There are 4 brass inserts, attached to PCB. On top they hold 3mm headless bolts (with inner hex key), which have conic ends (DIN914). Heater lays on cones and has almost zero direct contact. All this is tied with thin SS wire (available for vape)

  So:

  • We reduced down IR emission
  • We minimized direct heat transfer "by touch"
  • We can ignore down air convection

  The last thing we have to do - add PCB reflector, to minimize amount of landed IR waves even more. See image, aluminium adhesive tape (for thermal insulation jobs) will be perfect. After i used it instead of acrylic glass, result become almost ideal:

  • 25 min, 190C => PCB still below 50C. Stopped experiment, because good enough.

  Note, that's even with reduced bottom mirror, without external border. Also, in theory, bottom reflector should stay between heater and PCB. That's possible with additional intermediate PCB, but will increase height. I did not yet decided, should i use intermediate reflector or not. But you may be sure, current mount is already good enough, if used not 24x7.

  What's next?

  I have some ideas how to improve result and simplify assembly.

  Use Panasonic PGS as top thermal pad

  See EYGS091210 (size for 2 heaters ) and EYGS182310 (for 6 heaters). Those have HUGE thermal transfer (2x more than copper), and in theory can solve 2 issues:

  • Increase useable MCH area to full size
  • No need to paint top side

  Does it worth to pay 20$ more instead of black paint? IMO yes, if my experiment will succeed. With 50*50mm surface you can solder almost any hobby PCB.
  

  Pure PGS works up to 400C. Question is how to glue it to MCH. The most promising idea is to use cements for auto's exhaust system repair. Small amount of cement seems to hold well on MCH body, but i have no PGS to test all assembled with thin cement layer.

  Use real foil for MCH bottom

  I did quick tests, real alu foil is much better than silver paint. Unfortunately, i used Abro ER-400. Despite...

  Read more »

• Intro & requirements

  Vitaly • 10/19/2019 at 02:13 • 0 comments

  This device is trade-off for hobby use, if you need to assemble small PCBs from time to time. Of cause, it's not as good as reflow oven or bga reball station, but it's MUCH smaller.
  

  This project is not "new", and inspired by others like this one. Idea is to make device more useable and easy to repeat. That includes:

  • Simple assembly
  • More convenient power source
  • Nice GUI

  Components and assembly

  After searching aliexpress, found 50*50mm MCH heaters - maximal suitable of available in MCH segment. Plate temperature is not equal everywhere, so we should have about 30*30mm of working area. Not much, but not bad too. If you order boards with modern components, a lot of ones will fit such size with ease.
  

  Another point is to use PCB as mounting frame - put MCH & touchscreen on top, and everyting else on bottom. That requires experimenting with thermal insulation, but that's doable.

  With preliminary estimates, total size will be 130*70mm, 20mm height. Good enough to pretend on been small and convenient tool. You can see progress of PCB rework on EasyEDA page.
  

  Power

  Initially schematic was drawn for 220v power with small HLK-05 modules for CPU and triac control for MCH. But later i discovered USB-PD and decided to use it instead. Required power is 30-40W, easy to get from medium chargers. Result will be more compact and more safe.

  GUI

  This caused whole project to freeze for a notable time. I was searching open source libs, suitable to build advanced scenes and animations on resource constrained MCU-s. As a result - instead of doing my own projects, i participated in lvgl development. New version does nice font rendering and very soon will do subpixel smoothing (it's already in dev branch).

  But I'm finally back, and ready to move forward. May be you've seen dispenser project, been done in parallel with this one. It also uses lvgl and i already posted prototyped interface there.

  Let's go! In next log entry will share results of MCH thermal insulation, when been mounted on PCB.
  

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