SMD solder paste stencils are used to accurately “print” a thin layer of solder paste onto a PCB on which the components are placed before reflow soldering. The “printing” is done in a method similar to screen printing, where the solder paste is squeegeed through a 4 mil thick, stainless steel stencil onto the PCB.
This is all well and good, but commercial stencils are expensive, and are massive overkill for prototype boards. Here is a method for producing a “good-enough” stencil using aluminium sheet via a method similar to PCB production via the UV photosensitive film method.
Home-made solder paste stencil - [Link]
Unit is based on Arduino Atmega328P MCU, with over 430 UV LEDs. The PCB board is made using Toner transfer method and isn’t perfect. It was just too big and I was too lazy to do it again. However, marker here, scratch it there and it it good enough.
The unit itself is on single sided copper clad board, no additional cables, no narrow paths (except for one for power on the MCU). Design is straight forward. It’s designed to be powered from 12V source (computer) and take around 2,7Amps @ full power which means around 30Watts.
DIY UV Exposure Unit with LED and Arduino - [Link]
Haris Andrianakis writes:
After some modifications on my UV exposure box (scanner) for better UV expose, i desided that a better pcb must me designed for switch timer. The old one had over drilled holes and it was designed and built on my very fist steps. Also the high voltage side from the low voltage wasn’t seperated as it needed to be safe.
So i redesigned it in a more compact and easier to use pcb. The firmware has been also updated and now you can program the timmer by using the two buttons. The time is calculated by timer interrupt triggering using a 32.768KHz RTC Crystal with better accuracy. The display update also has been changed from static to dynamic.
PCB Exposure Switch Timer V2.0 - [Link]
This device is a countdown timer specially designed for PCB exposure box.You can set how many minutes will be on UV light device , store this time in PIC’s EEPROM . Pressing start button lights are on until preset time ends. When lights are off an audible signal is heard. Microcontroller used is Microchip’s PIC 16F877. I used Mikroelektronika Mikropascal compiler to program the chip. Delay time 1-255 minutes.
Count down timer for UV PCB exposure boxes - [Link]
Giorgos Lazaridis writes:
I got myself some UV-curable solder mask for my PCB workshop, and as soon as i got it, i discovered that my UV artwork transfer box is totally incapable to activate the UV paint and cure it. I began searching the net for powerful UV lamps, and then it hit me: Some months ago i uploaded a theory regarding the Cold and Hot cathode discharge lamps. During my research for these lamps i found out that they can provide directly visible light (lamps without internal coating), or they produce UV radiation. The lamps that produce UV radiation have an extra coating on their internal surface which glows when excited by the UV rays, thus producing light!
Hack a Hg Lamp to a Powerful UV Light Source - [Link]
I am using a positive photo-lithographic process to transfer the artwork to a photosensitized, copper cladded PCB laminate. Positive means, that during the development step the protective coating on the copper is removed in those places that were previously exposed to UV light. So the artwork has to block UV light where you want the traces on the board.
How you can make perfect PCBs yourself – [Link]
Nice project from Petar , he send me some photos of his UV Box. This UV LED Exposure Box was published in the magazine Emiter, and here’s what the author says on this project.
My UV box contains 54 ultraviolet 5mm LED distributed in a matrix of 9X6 leds. The box can enlighten board with maximum dimension of 12X18cm. Built-in digital timer allows programming of the desired time for lighting.
Keep away your lights from direct UV light from box. Wavelength of the LED is the same with the sensitivity of the UV spectrum of photo spray Positive 20.
UV LED PCB Exposure Box – [Link]
This project is a UV exposure box with timer using small UV florescent tubes. Instead of purchasing a tube with ballast the author used the small ballasts from florescent fixtures. He also added a timer to control the exposure time precisely. [via]
DIY Circuit Board UV Exposure Box with Timer – [Link]
This project shows how to build a PCB UV exposure box using UV LEDs and digital multifunction timer. Check details on the link below.
PCB Photographic Artwork Transfer UV Cabinet – [Link]
Jacques Lebrac build a UV LED exposure box using only one LED. The led used is a 5W unit, emits at 400 nm UV and needs 1.5A of current. As a heatsink he used an aluminum arm that also supports the LED on proper distance. A LM117 is used to regulate the power driving the LED. [via]
Single LED UV PCB exposure box - [Link]