Above is a video detailing one method for populating a two sided surface mount PCB. We covered using a stencil to apply solder paste for a PCB a few weeks ago. In the comments there was a debate about the virtue of using stencils as well as a question about how two sided boards are populated. This was a good question because reflowing a board twice can cause components on the underside to fall off.
[Wim L's] comment mentions that there are a couple of methods for two sided population. In the video you will see that a stencil is not being used, but instead, paste is applied by a pedal actuated syringe. The paste is applied to the underside of the board first, then a teeny dot of epoxy is added to hold the component in place. Each part is then positioned normally and baked in a reflow oven. This process both reflows the solder, and cures the epoxy. When the board is reflowed a second time, the epoxy holds the bottom components in place as the top solder reaches its melting point.
This method of applying solder paste is slower than using a stencil. But if done correctly, every component can get the amount of solder needed.
[Oleg] is the creator of the USB Isolator and therefore has a need to frequently populate the same board. He’s using an acrylic frame that fits the PCB perfectly to hold it in place so that paste and be applied right up to the edges of the board. He ordered a laser cut Kapton stencil for applying the solder. The paste is squeegeed into the stencil holes, the stencil is removed, and parts are placed with tweezers and a steady hand. For the final step, the boards go into an old toaster oven for reflow.
[Oleg] uses temperature marker on his boards to monitor the progress of the reflow. This marker is basically a crayon that begins to melt at a specific temperature. When the board has cooled, the melted mark can be scraped away or removed with alcohol.
Of course this is only really useful if you have a bunch of high-quality boards to populate. But with the relatively low cost of getting professionally made boards we think the need for this type of assembly process is on the rise.
After hearing that his video card might be repairable by heating it up to reflow it, this user did just that. He stripped it down and tossed it in his oven. It’s amazing how often this type of hackish repair works. We’ve heard of people using candles on ibooks, tossing video cards in oven,s and wrapping an xbox 360 in a towel and running it for 30 minutes to get it hot enough to reflow itself. Why even bother with controlled temperatures and exact measurements? What other crazy fixes have you had to employ? We had a Playstation that only worked upside down.
Joystiq has been tracking the new starlet of Xbox 360 failures: the E74 error. It appears as the lower right light on the console turning red and an on-screen message telling the user to contact support with the error E74. The number of reported E74 errors seems to have risen since August 2008 and people are wondering if the more recent increase in errors are related to the release of the New Xbox Experience (NXE) Dashboard update. Did Microsoft reclass Red Ring of Death (RROD) failures as E74 to avoid warranty replacements? Read the rest of this entry »
[mightyohm] put together a nice piece of lab kit. It’s a PID controlled hot plate. The plate is capable of reaching 500F, hot enough to do SMD reflow soldering. The large chunk of metal has a hole drilled through the center to contain a cartridge heater. A thermocouple is used to monitor the temperature of the plate. Ceramic standoffs separate the plate from the rest of the device, but he still needs to come up with a way to stop the radiant heating. The control box houses the surplus PID controller along with the power switch and solid state relay (SSR).
Here’s an interesting kit put together just to help you work on your SMD soldering skills. It’s got 49 SMD LEDs on the front with a programming header and switch jumper. The back has an ATtiny26L and a coin cell. At only 3V, power management is essential; all of the example programs are only addressing one LED at a time (imperceptible to the human eye). If you turn on too many LEDs at the same time, the voltage drop could cause the AVR to reset. Included example programs are a scrolling marque, bouncing balls, and Conway’s game of life. SparkFun has tutorials for regular SMD soldering and using a reflow skillet. The video below shows the kit builder attaching just one LED using the heat and slide method.
MightyOhm’s laboratories have recently decided to start tackling more surface mount work. As part of this upgrade to SMD hot air reflow stations, they’re handling a lot of solder paste. Solder paste is happy at less than 50degF and above freezing, and [Jeff] didn’t want to chance that lead infiltrating his Manwich, so he built this solder paste fridge. The main unit is a standard 12V peltier based travel cooler. He attached a surplus PID controller with a K-type thermocouple to maintain the temperature while preventing the cooler from being always on. The only adjustment he really had to make was adding a bleed resistor to force the MOSFET to turn off. You can find more pictures of his project on Flickr.
I was poking around spark fun electronics, and came across this interesting walk through showing spark fun’s solder stenciling technique. (I’d put on some gloves before handling that much lead paste) They top it off with some alternative ways of doing reflow work. My favorite has to be the target hotplate method. It’s a nice introduction if you’re interested in doing SMD work to save money and space on your projects [but not sanity. say goodbye to that] Me? I’ve used a 15 watt weller with a dremel modified small tip. It works great if you’ve got some one of those syringes of heat activated glue. Place, bake and solder.
