FIXING TEMPERATURE SENSORS

April 28, 2014 in REFLOW SOLDERING

This post is about how to assure that your oven temperature sensors are always on contact with the pcb we want to solder.

One of the most important things about soldering everytime right is the hability to maintain a consistent contact with the pcb your want to solder and your temperature sensor during the whole process. It happens sometimes that the sensor is not contact with the pcb, if this is the case the profile will not be always the same. See the following graphs.

temperature graphs1

Every graph correspond to a real soldering process, as you can see they are pretty uniform even if they were done in different days. The yellow one is different from the others, the soldering process is longer and quality of the soldering was not the same. The difference is that the sensor detached 1mm from the surface of the PCB 20 seconds after the soldering process started. This made the sensor take more time to heat as it was not in contact with the pcb.

It is not easy to maintain the contact of the temperature sensor to the pcb during soldering, we can not just put a sticky tape over the thermocouple to glue it to pcb as the pcb surface is full of solder paste and not soldered components so this is not possible. We decided them to build a clamp that maintained the contact as a resort, but this is not easy in an oven reaching 250ºC, also the clamp must be narrow to avoid shadowing parts of the circuit to solder. You can see our clamp here.

SENSOR OVEN WITH PCB

SENSOR OVEN WITHOUT PCB

It is quite easy to build one, you will need a rigid ground cable, heat resistant Kapton tape, aluminum tape and a K-thermocouple.

First you will need to take some rigid ground cable and strip the isolation from it leaving only the rigid copper wire.

TEMP CABLE

TEMP CUT CABLE

      TEMP CABLE STRIPPED

Then you can attach the thermocouple with kapton tape in one end of the copper wire and them on the other extreme at the length you would like to have for the sensor:

TEMP KAPTON1

TEMP KAPTON2

Now you can build the “feet” of the sensor by turning the copper wire to give it the form of a feet. This avoid the sensor to turn once installed in the oven.

TEMP TC+CABLE+FEET2

The last step is to cover the sensor and the cable with aluminum tape, this will protect most of the sensor and reflect quite a lot of the infrared emissions.

TEMP TC+CABLE+FEET+ISOL

And now as you can see we can assure a perfect contact during soldering using the kapton tape to maintain a little tension on the arc of the wire.

TEMP FINAL

NEW FEATURE: USER DEFINED SEQUENCES

March 18, 2014 in REFLOW SOLDERING

We have added a new feature to our PC program v1.2, user sequences.

This means that from now on you can create your own sequences of phases and save them in the hard-drive of your computer to run them later. This is handy if you want to do non standard soldering recipes or to use your controller as a temperature controller for anything different from a soldering controller.

Here it is our new sequence editor:

NEW2

So in the combo box “Phase type” you can select the type of phase you want to add, you can select from:

  • Time limited and temperature controlled PID:

This type of phase will start the  % PID regulator so it will try to arrive as fast as possible the target temperature in the “Temperature” Textbox. Once reached the temperature will be maintained for the “Time” in seconds stated in the Textbox.  The “Max Time” Texbox will define how much time in seconds we will try to arrive to the PID target temperature, if the temperature is not reached in this time the sequence will be stopped and an alarm will be issued.

pìd

  • Time limited PWM:

This type of phase will trigger the fix % PWM rate in the “PWM rate” Texbox.  This PWM will be maintained for the “Time” Texbox seconds. The sequence will be aborted and an alarm issued if we go over the “Max Temp” Texbox temperature.

PWt

  • Temperature limited PWM:

This type of phase will trigger the fix % PWM rate in the “PWM rate” Texbox.  This PWM will be maintained until the “Temperature” Texbox temperature is reached. The sequence will be aborted and an alarm issued if we go over the “Max Time” Texbox time in seconds before reaching the target temperature.

PWM

  • Time limited Wait:

This will just stop all during the time in seconds in the “Time” Textbox .

WAI

  • Restart:

This will restart the sequence automatically. Use this function with caution as it will run in loop the sequence until manually stopped. No parameters for this phase.

RST

  • Time limited PWM in Out 2 (WORKS ONLY IN CONTROLLERS WITH FIRMWARE OVER v.28):

This type of phase will trigger the fix % PWM rate in the “PWM rate” Texbox, but this time only in the Output 2 of the controller.  This PWM will be maintained for the “Time” Texbox seconds.

PWM2

You can add phase by phase using the “Add Phase” button, this phase will be added to your sequence. You can see a summary of your complete sequence in the “Sequence Summary” Texbox. You can also delete a phase in the sequence by typing the number of the phase in the Texbox next to the “Delete Phase” button and hitting the delete button.

Once you have defined your sequence you can save it with the “Save Sequence” button, it will be stored in a txt file and you can open it later using the “Open Sequence” button.

To  Start a sequence just hit the “START SEQUENCE” button, the sequence will be executed and once finished it will be stopped automatically. If you want to stop it before the end you can use the “STOP SEQUENCE” button.

complete

Another new feature of this version of the program is on the PWM tab. Now you can also start a constant PWM test in the second output of the controller. Just type the PWM rate in the CYCLE Textbox and hit Start in the PWM2 “Start” button. Unfortunately this feature will only work in controllers with firmwares over v.28.

pwm_test

Hope you like it.

USING STENCILS

March 16, 2014 in REFLOW SOLDERING

Hi, this post is about stencil usage.

Stencils are the best way of applying the correct quantity of solder paste to the pcb pads before using an oven to solder components. Other methods include syringes or paste dispensing pneumatic systems, the problem is that they are much more slower and the quantity of paste is difficult to adjust.

So what is a stencil, a Stencil is a laser perforated thin sheet of material (usually stainless steel but you can find then in plastics also). The holes in the stencil have the same fooprint as the pads of the pcb so to apply paste you just have to put it in one side of the stencil and them apply it with a squeegee, It is easier to see in the following photographs.

The advantages of the stencil is that in some seconds you apply solder paste to all the pads so you don’t have to pass many hours applying paste pad per pad with a syringe, and the quantity of  paste is always the correct one. Using a stencil will reduce the quantity of shorts between pads and other usual problems when using reflow soldering.

The main disadvantage is the cost. Stencils are only valid for one particular PCB so you have to order one for each different PCB you want to solder, it is not a problem if you are going to solder 100 times the same PCB but it is too expensive for only 1-2 prototypes. Also the alignment of the PCB with the stencil is really critical so you would need to use some sort of holder for both the stencil and the PCB which fix both together and don’t leave any gap. These are called “stencil printers” and are quite expensive, normally around 400 to 2000 euros depending on the quality. You can see an example from eurocircuits below.

eC-stencil-mate

Personally I use a low cost solution which I find really good and less expensive. It is the eurocircuits EC-Stencil fix instead of a stencil printer. When you order a pcb and stencil in eurocircuits you can order them  EC-registration compatible, that means that it will be supplied with exterior centering holes you can use to center it in the Ec-stencil fix, a board that helps to keep the stencil in place while applying the solder paste.

So here you can see how it looks:KIT

 

Now we use the centering pins for centering the PCB and the stencil.

PINS_EXP

 

I center my PCB using the botton pins:

PINS2_LOW

I center the stencil over the PCB using the pins:

DSC_0222_low

Next phase would be to add the solder paste:

paste1_low

Now in a single pass with the squeegee I add apply the solder paste to the pads:

paste2_low

The results as you can see in the photos are quite impressive for something as simple as this.

ste_final_low

You can find lots of videos in Youtube about this ec-stencil, how to use it, fix it… etc.

This is not the only low cost stencil system in the market but it is the one I use and I am pretty happy with it. I have seen others worth trying like fixing stencils with magnets (http://www.beta-estore.com/rkuk/order_product_details.html?p=64) .  If you have experience with other methods please contact me so we can share it with everybody.

NEW CONTROLLER BOX

February 17, 2014 in REFLOW SOLDERING

Our controller is designed to be fitted in a standard blue translucent box. This box is really convenient due its low cost and small size but it has also some limitations.

The standard blue box is 2 cm high, this is the limit between shipping a packet and a letter. The cost of shipping a packet is 7-8 times higher than shipping a letter. For international shipping we can end up paying 15-20 euros per shipment, which is quite high for a controller designed to be powerful but inexpensive.

BOX_small

Also this standard box comes without holes and cutting nice holes in ABS is tricky, the material tends to melt when you try to cut it.

We have been looking for a solution to this since the firsts controllers were shipped, but we have not found a small, yet cheap box who fits our controller.

That’s why we have decided to develop our own controller box. The new box is a 3D printed box made in translucent plastic so you can see the status leds though it, and  it is only 15mm high so it’s OK for low cost shipping. It is also designed to fit perfectly our controller.

hand_1_low

Another advantage of this 3D printed approach is that if you have a 3D printer you can print it yourself, the files are HERE in STL format. I recommend using at least 0.2mm resolution to have better looks in your controller.

abierta1_low

If you don’t have a 3D printer just ask us for the box, it is not expensive at all and it will help also to protect your controller during delivery.

dos_1_low

UPDATE: BUILD YOUR OWN REFLOW OVEN

December 10, 2013 in REFLOW SOLDERING

When I made the post about building a reflow oven and the one about temperature uniformity I explained that my oven was heated using five 200Watts heating lamps. This was not enough when using a fan to recirculate air inside the oven to improve temperature uniformity as the heat loses higher than expected.

We have made some modifications on the oven to avoid these problems:

  • Firmware changes. These involved changes in the PID controller programming and the way heating ramps  starts. We will give you more information in another post.
  • Add 3 more 200Watts heating lamps. So the oven is now equipped with a total of 1600Watts of heating elements. 8 lamps
  • There is a turbine below the oven that injects fresh air when the process is finished to cool down the PCB faster. This turbine has been changed to a small high static pressure turbine instead of the low power, low pressure old turbine. This has significantly improve cooling speed.

turbine

  • When the soldering is finished a solenoid linear actuator opens a hole at the top of the oven to help the hot air leave the oven. This solenoid has been changed to a new one with much larger linear movement.

electromagnet

 To see if the modifications improved the oven we did some tests:

UNIFORMITY TESTS:

We repeated the test we made with the old oven. We measured the temperature sensors in 4 places distributed inside the oven to see if the temperature was uniform.

   Uniformidad

As you can see in the graph the results were quite good, the temperature is really uniform during the soldering process. The only point a bit different is the “T4″ during cooling phase, this is because this sensor was just over the fresh air turbine we use for cooling down but even this point has a decent uniformity. You can see our previous post about temperature uniformity here.

MAX SPEED TESTS:

As we have added more power to our oven so we expected being able to heat the oven much faster. To test that we ran two soldering processes with 100% ramps. Running two tests also allowed us to test repetability.

repetibilidad

So a whole soldering process in less than 200 seconds, that’s fast. Anyway, this was just to test the oven don’t try to solder components like this or they will be fried.

CONFIGURE THE OVEN

Now that we were pretty sure the oven was working we decided to search for the correct soldering parameters for Lead free solder.

There are many places were we can find good guidelines for reflow soldering. I would recommend:

 

After reading this my targets were:

- Flux activation phase, between 150-200°C for 100 seconds, commencing at 150°C and reaching slowly 200°C at the end of the phase.

- Wetting time, time over 217°C, not exceding 60 seconds.

- Max temperature 245-255°, about 15 seconds.

- Max heating ramps of 3°C/second.

- Max cooling ramps of 6°C/second.

Now it is a matter of trial and error, I placed a dummy PCB board on the oven and the controller temperature sensor on the board and started to make trials until I was satisfied with the result. Don’t make your tests inmediately one after another, you have to let the oven cool down completely or your results will not be repeatable next day when the oven is at room temperature.

So here you can see the results for the soldering with 100% ramps (blue) and the one with the final settings I chose (green):

soldadura final

As you can see my green profile matches all my targets. The controller parameters were:

Ramp 1: 55%.

Temperature 1: 195°C.

Ramp 2: 70%.

Temperature 2: 255°C.

Time 1: 50 seconds.

Time 2: 15 seconds.

Time 3: 120 seconds.

Remenber that in our controller these parameters mean:

Parameters

You can find here all the information about our reflow controller and how to use it. More information about our controller software here.

The use of a dummy board is necessary as the performance of the temperature sensor is not same over a PCB board or holding loose in the air. In a perfect world oven suppliers recommend to use the actual board you want to solder to fine tune your oven, but as this can be difficult for small quantities just use the most similar board you don’t mind to destroy during testing.

 dummy board high res

 

To visit our first post about building a reflow oven, go here.

BUILDING YOUR OWN REFLOW OVEN

September 13, 2013 in REFLOW SOLDERING

Until now we have talked about using standard toaster ovens to build reflow ovens, but if you have a little experience in building things and you have some equipment you can build one from scratch.

Mine is not really good looking but it works really well:

DSC_0079

I don’t intend to do a tutorial on how to build an oven but this can give you some ideas.

We have build one using the following components:

- MakerBeam beams and brackets for the structure. Check them in www.makebeam.eu, they are perfect for building modular structures.

- Aluminum sheets of 0.75mm. They are easy to fold and cut so they are perfect for making the “skin” of your oven. My recommendation would be to use this cutting circular saw you can attach to Dremel mini-drill, see photo.

2303

- Heating infrared lamps. I have used Osram Halotherm lamps, in my case 5 pieces, 200W each. I will probably add 3 more as the power is quite low when using a fan for heat distribution, see my previous post about this issue.

- Holders for infrared lamps.

- A piece heat resistant glass to make the window of the oven. In my case I used Neoceram glass which is perfectly good for more than 300ºC.

- Various Electrical materials (cables, connectors, isolation tape…etc).

- Aluminum sticking tape. Ideal for closing gaps in your structure once made. You should use the one that can withstand 250ºC at least.

- Fire stop Mastic, I have used the one from Sika “FireStop”. You can also use heat resistant Silicone, I have used Sika “Firesil-90″. The heat resistant silicone is easier to handle and it is a little bit flexible but it is good only for temperatures below 300°C, the heat resitant mastic can withstand higher temperatures (1000°C).

First thing would be to mount the oven top structure, this is where lamps are mounted. I definitely recommend Makerbeam for building the structure, it is really easy to use and you change it as many times as you want. The initial structure look like this:

foto estructura superior_lowNext thing is to prepare the lateral closing panels that will support the lamps in place.

DSC_0163

soporte lampara 2

Next would be to install the laterals.

foto cerrado

You can use the heat resistant mastic to close the gaps between the aluminum parts:

foto mastic

I also added a lid that acts as an isolator limiting the heat loss and reducing the danger of burning yourself.

DSC_0151_low

DSC_0152_low

 

Mount the lid over the lamp support structure and close the gaps with the aluminum tape.

DSC_0136_low

So the top side is finished. The lower side structure is also built using Makerbeam profiles.

DSC_0134_low

This part includes all the electronics: controller, solid state relays, an oven fan for distributing the heat…etc. All is below the oven to save some space.

DSC_0132_low

Put the two parts together, install the lamps in the holders and the oven is ready.

horno entero_low

Here you can see the lamps mounted on their holders.

lamparas distribucion_low

There is a new post about building a reflow oven, see it HERE.

TEMPERATURE DISTRIBUTION

July 8, 2013 in REFLOW SOLDERING

This post is about temperature distribution in homemade reflow ovens.

When developing a reflow oven or simply transforming a toaster oven into a reflow oven we ofter have doubts about temperature uniformity. Will my new oven have an even temperature distribution which will allow me to solder bigger pcbs?.

We have made a simple experiment using one homemade reflow oven to see if the temperature was uniform.

Our test oven is a simple oven equipped with 5x 180W  infrared lamps evenly distributed. This distribution should allow to have already quite good heat distribution.

horno entero_low

lamparas distribucion_low

 

Our next step will be to distribute temperature sensors on the inside of the machine to be able to record their temperature at the same time.

DSC_0099

Now we can start soldering. We will repeat the soldering process two times to see how temperature distribution is inside the oven with and without an fan for forcing the air to move. For the results see the graphs below:

The sensors marked with a “B” are showing the temperature with ventilator

Graphique 4

So the effect is that the uniformity of the oven with fan is much better but the oven is much more slower and heat looses are much bigger.

So if you oven is not really powerfull and you can not upgrade it you will have problems when soldering as the heating ramps will be much more slower. Take that into account when building your oven.

On the other side your oven will have a much better temperature distribution inside when using a ventilator, even with ovens equipped with infrared lamps this effect is quite clear. My oven have lamps evenly distributed an even like that some parts of the oven are 20°C cooler than others.

UPDATE (10/12/2013): We have added more power to our oven, if you want to see the results go here.

SOFTWARE

June 10, 2013 in REFLOW SOLDERING

N_electronics control software allows you to control all the features of the oven in real time and modify also soldering parameters.

For example you can:

Slide6

- Simulate any PWM rate.

- Program and store 4 different soldering programs.

- Test your PID controller settings in the special PID mode.

- See the current soldering graphs while soldering.

 

 

 

 

 

 

This software is compatible with any Windows running PC.

Slide2

 

Slide4

CONNECTORS

March 26, 2013 in REFLOW SOLDERING

vertical_conectoresEasy to connect and disconnect plugs. 8 screw poles connector with access for:

  • One input for a K-type thermocouple temperature sensor.
  • 2 digital 0-5v outputs.
  • 2 GND.
  • 2 5vdc outputs.

There is no connector for a power supply as the controller is directly powered by the USB link with a computer.

ASSEMBLY

March 21, 2013 in REFLOW SOLDERING

desglose_componentes1Our controller is designed to fit in a standard box so it will be protected from dust, ESD and mechanical damage. The box is transparent so you can easily see the status leds indications though it.