This update in the LED Road Test explores reflow soldering of Würth Elektronik power LEDs. Reflow systems generally try to use a temperature profile to heat the work up to soldering temperature. Here is a plot of a typical thermal profile:
This profile has several purposes such as minimizing thermal stress, evaporating flux and melting the solder without overheating the components.
My first test will be using a heat gun to heat up the substrate from below.
I start by doing a dry run to get a feel for how close the heat gun needs to be to obtain various temperatures.
Next I apply solder paste to the circuit board and position the LED on the solder paste. This is actually very difficult to do without a solder stencil, I used a toothpick and a needle to apply paste under a microscope. I wouldn't want to do a lot whole PCB like this – it is not only laborious, it would be prone to inconsistency.
Then it is time to reflow the solder:
It is probably apparent that it is hard to control the temperature to follow the ideal profile closely, but with a little practice it should be possible to get close. This was my first attempt and it seemed to work well enough – much better than my previous attempts to use an iron.
This technique works well enough that I would not hesitate to use it again, the main issue is applying the solder paste. I will have to ponder how to do that more effectively.
I had intended to try another reflow technique based on induction heating, and I will as soon as I get access to an induction heater, but it may not happen before the submission deadline for this road test. I am quite hopeful that induction heating will make it even easier to control the temperature profile because you can simply punch in the desired temperature without worrying about how close to get the heat gun.
If I don't get access to an induction heater and don't think of any more additions to the road test, this blog will conclude my road test.
This road test was my most extensive road test so far - it entailed producing 16 blogs and 20 videos. The project had the usual issues with delivery of components that occurs with most multi-faceted projects, but there was always lots of things to do.
The road test kit was useful for many interesting applications and it was a lot of fun researching and experimenting with about 40 LED applications. I learned a lot and most of what I tried turned out very successfully.
Thanks to Würth Elektronik, Texas Instruments and element14 for sponsoring this road test.
The LED Road Test page is here:
http://www.element14.com/community/roadTests/1481
The Lighting Group page is here:
Here are links to my other blog entries for this road test:
LED Road Test - Proposal - Blog 0 Jan 1, 2016
Light Emitting Diodes Road Test - Blog 1 Nov 1
LED Road Test - 3D Printed Housings - blog 2 Nov 10
LED Road Test - Dodecahedron Light Fixture Blog 3 Nov12
LED Road Test - Wearable Interactive Lights - Blog 4 - Nov 13
LED Road Test - Interactive Trophy - Blog 5 Nov 16
LED Road Test - Making Household Objects Interactive - Blog 6 Nov 22
LED Road Test - Power LEDs - Up & Running - Blog 7 Nov 24
LED Road Test - Star Wars - The Force Awakens - Blog 8 Nov 28
LED Road Test - Selfie Phenomenon - Blog 9 Nov 29
LED Road Test - MSP EXP430FR4133 Launchpad IDE - Blog 10 Dec 6
LED Road Test - Vehicle Situational Awareness System Blog 11 Dec 14
LED Road Test - Vehicle Situational Awareness System Indoor Demo - Blog 12 Dec 20
LED Road Test - Maple Leaf Christmas Decoration - Blog 13 Dec 24
LED Road Test - Reflow Soldering Power LEDs - Blog 15 Jan 10
LED Road Test - Induction Heating Reflow Soldering - Blog 16 Jan12
LED Road Test - Summary - Blog 17 Jan 15
Associated Video Links
Creating a Light Fixture using 123D Design
Wearable Interactive Arc Reactor
Interactive Illuminated Household Objects
Star Wars - Let The Force Be With The Light
Vehicle Situational Awareness System in Operation
Vehicle Situational Awareness System Operating at Night
Induction Heating Reflow Soldering
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