Completed Project 200°C SMT Hot Plate

Thread Starter

Wendy

Joined Mar 24, 2008
22,646
SMT Hot Plate F.jpg
Something I learned as a machine maintenance tech in a clean room is preheating a part to 200°C Makes it much easier to solder. I designed and made several for the production line for this purpose. So designing this one just more of the same. My stroke left me unemployable so cost was a major factor with this design. Wood is cheap and surprisingly temperature resistant and insulative. 200°C will char it but doesn’t seriously damage it.

First step is to get the sheet metal. I got a .01” x 12” x 12” sheet metal and used the following pattern to cut 6 metal spacers shown in the .png file (print this pattern using M$ Paint and the individual sheet is to scale). You will also need a piece of ¼ thick aluminum for the top of the hot plate. I countersunk and tapped the holes for a #6/32 screw. This is important, as it will simplify construction later. Also drill a 0.1” hole in the side of the back of the top plate as deep as you can to immerse the thermocouple into. I used high temperature RTV to make it stay in place. So after cutting and drilling the spacers to spec I started assembly. The 1.0” x 1.0” notches give the square bumps on the heater spaces to go when stacking the heater elements (Qty 4). You will also need a separate unnotched bottom plate. Assemble as shown.

After you are done stacking the metal plates (spacers) and heater elements (Quantity 4 of each) unite the hot assembly the with a #6/32 nut, this will form a space between the wooden base and the heater assembly (which will char the wood less later).
0 Stacking hardware.jpg
You may want to add a washer to try making the heater assembly sit flat on the wooden base (even with the notched spacers the heater elements bulged a bit.
2 Partial Assy.jpg
The wooden base will need 6 holes for my #6 wood screws. Label each hole with the terminal number,

Do yourself a favor and crimp the lugs on before starting the stacking phase and if you are real adventurous cut the lead lengths too (I’m chicken and used the entire wire length). I labeled each lug with the resistor number matching the terminals shown on the schematic. I also labeled the terminal holes on the base block (hidden hidden below the lugs) for easy reference. Take the time to add spacers as needed to level the total hot plate assembly and match the heights of the wrap around wooden frame. Mostly this is for appearance.
1 Wiring.jpg
Schematic.png
Schematic
Then wire the hot plate as shown.
1 Wiring.jpg
After I was done I used a hobby stick to flatten the wires
Bottom.jpg

A quick note about the power supply, you can use a 24VAC transformer and a commercial proportional power controller in lieu of a variable power supply. Since I do have a variable DC power supply that is what I used.
4 Power Supply.jpg
It took 22 minutes for this unit to hit 190°C, I adjusted it to 18.75 VDC (78%power) where it stabilized to approximately 200°C.
When I turned it off in 1hour 10 minutes the hot plate cooled to 60 °C. In 3hours it was 28°C. Now you know why the timer was in the picture.
 

Attachments

Last edited:

Thread Starter

Wendy

Joined Mar 24, 2008
22,646
BOM
Qty Description
4 .....0.1” Spacer Plates (download "SMT Hot Plate v3.png)
1 .....¼” Surface Plate I bought a 4" x 4½" x ¼" aluminum sheet (I bought mine from Metal Marketplace.
1.....0.1” Bottom Plate
4.....Heater Mats
2 .....#6/32 x 2” counter sunk flat phillips head screws
4 .....#6/32 nuts
2 .....#6 small washers
2 .....#6 split ring lock washers
1.....¾” x 4” x 4.6” Wooden Base (I used plywood)
4.....#6 x ¾” pan head wood screws
4.....1” square ¼” high rubber feet (highly recommended!)
4.....25W 12V Silicon pad heaters18[wh].....[/white]#6 crimp on lug ring terminals

.......Wire to carry up to 4 amps 20 Ga or better.
1.....24V 4A Power Supply (variable preferred)
1.....Type K thermocouple and meter
 
Last edited:

Thread Starter

Wendy

Joined Mar 24, 2008
22,646
Ewww, that's just wrong.

Did you click the link in in the BOM? Store bought parts are hyperlinked. It's kinda my thing.
 
Last edited:

ErnieM

Joined Apr 24, 2011
8,196
Nah, I copied "Silicon pad heater" from the BOM and searched on that to get general info.

MY EYES!!! MY EYES!!!
 

metermannd

Joined Oct 25, 2020
232
Well, that's worse than when I was doing a search for an obscure Westinghouse electronic assembly on the E place and finding a "sponsored link" for maternity bras right in the middle of the search results!
 

ErnieM

Joined Apr 24, 2011
8,196
A few years back while working for a place with a very strict pr0n policy I searched for some compounds by Emerson & Cuming.

I clicked the first hit without reading... OOPS
 
Top