Posts Tagged ‘assembly’

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Cheap eBay reflow oven

2013/04/25

I recently got a T-962 reflow oven from one of the many front-ends for the same fulfillment shop in California that sells various Chinese imports.  The unit cost $240 with free shipping, and arrived in roughly a week.  It’s the smaller of the two available units, the B model having a 1000W element rather than 800W, and a somewhat larger overall work space.  The unit came shipped in the usual Chinese style: wrap the unit in enough bubblewrap to fill the box on its own, stuff into cardboard box, then add about as much tape by weight (waterpoofing?).  The build quality is reasonable enough at first glance.

I started out with a few small boards (my Xmega DIP adapters) and went with “wave 2” designed for 63Sn/37Pb, peak temp of 225C.  Right off we have our first problem: the UI is horrible.  The screen itself is fine, but the font used is nasty.  The buttons are OK physically, but they’re only scanned once per second(!), which means you have to hold them down until it decides to notice.  Unfortunately, it doesn’t do any state latching, so if you hold it down a little too long, it’ll treat it like another button press.  Apparently debounce and interrupts are too complicated.  Even worse, when exiting some menus, it immediately processes that button press again.  A prime example is anything that uses F4 to return to the main menu: main F4 means “switch languages”….

The next problem is that while there’s a “cool-down” fan in the back, some genius decided that it should blow in to the chassis.  This results in all the solder fumes being pushed out the open bottom of the oven, and into your local atmosphere.  My absolute first modification to the oven will be turning that fan around.  I then need to find a flange with screw mounts for a 4″ flex-duct, at which point I can route the exhaust into my theoretical wall vent and continue breathing actual oxygen.

As you might expect, I took the unit apart to figure out what all is inside.  The answer: an insane amount of very tenacious hot-glue.  They hot-glued everything.  I spent a chunk of time removing all the hot-glue, because it was unnecessary (now that it’s shipped to me…) and because I wanted to actually be able to disassemble it.  I didn’t take any pictures the first time I took it apart, I’ll have to do so again and get all the detail I need.  Unfortunately the fan that needs to be reversed is buried inside several more layers of insulation and silver (duct) tape.  I didn’t dig that far into it yet because I actually need to make certain it’s usable for a while still…

The main board is designed to be split, with the various power stages on one side and the logic on the other.  The MCU is an LPC2134 (ish), with a funky programming header (1×6?) nearby, which bodes well for fixing the firmware stupidities.  A full reverse-engineering of the board will be necessary to figure out all the I/Os, but it doesn’t look like it’ll be a huge challenge.  The good news is that everything looks to be easily controllable, so enhancing the functionality with new firmware should be easy enough.

Just now I did a “large” panel of PCBs, taking up most of the available working space.  Here we find another issue with the oven: it’s not very even.  The panel had a 4×4 grid of boards, and the front row didn’t really come close to soldering in the preprogrammed “wave2”.  I had to not only switch to manual and keep the peak temperature in place for quite a while, but I had to open the tray and very carefully rotate the entire panel 180deg in order to put the unsoldered boards in a hotspot.

New firmware could fix this by running the “cooldown” fan at a very low speed during heating cycles.  The bottom of the unit might need to be taped up in order to force incoming air to enter from the front of the chassis and pull across the boards, though I haven’t looked at the bottom much.  The other advantage of doing this is that the “preheat” stage where the flux fumes start to off-gas would be exhausted to the outside.

At some point when free time actually exists, I’m hoping to hack up new firmware (after swapping out the chip if it’s code-locked, so I don’t kill it completely) and make it a bit more viable.

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Fully-assembled boards

2011/06/07

I got a call yesterday that triggered a mad dash to try to get to Canby by 5pm to grab the freshly assembled PCBs.  Not sure they wouldn’t have answered after 5pm, but didn’t want to take the chance, eh? ;-)

The only error was actually caused by Digikey, where somehow they managed to stick a cut tape of some random SOT23-5 part inside a bag marked for SC70-6 parts…  I’ll have to figure that one out with them and mount those parts myself.  Luckily those are on the controller boards, of which there are only 3.

I have to assemble the 3rd board of each stack myself, because I ran them on the DorkbotPDX group order.  That’s because they’re simple by design, so I can run variations more frequently (and cheaper) as I work on fine-tuning that part of the product.  That and the debug board (which I have to solder a cable to) bracket the above boards, making the whole thing quite colorful ;-)

Part of my design is careful re-usability of parts.  The interface boards I’ve designed for upgradability are also snapped onto the controller, so if I come up with a better version I can replace the controller’s interface just as easily as all the others.

The next step of course is to bootstrap them, which is always a very nerve-wracking procedure…  It begs the question though: if the boards are red and purple, what color of smoke should come out if something goes wrong???

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Panelizing PCB & Assembly: prepping the boards

2011/05/26

In my quest to get a group of PCBs fab’d and assembled as inexpensively as possible, the first step of course is getting the artwork for the individual PCBs ready.  Once the schematic is finalized and the basic layout is done, additional steps need to be taken in order to make then panel-friendly, and actually get the artwork together into one chunk.

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The joys of PCB & Assembly panelization

2011/05/24

I’m working on the latest round of prototyping for the product I’m working on.  This time there are a number of factors that are forcing me to change from my previous development methodology.  First and foremost, there’s a lot more pressure to get it done fast rather than cheap, so a major factor is the reduction of unknowns like low assembly yield that were making the process rather slow.  Second, I’ve shuffled things around in the design in ways that both call for tighter design rules than the DorkbotPDX group order provides, and make assembly even trickier to do by hand.

The project itself consists of a whole series of different PCBs.  The main group of 3 boards stack on top of each other, while the controller has a site to stack on the top board from the first stack, then itself live on a larger board that I haven’t finalized yet.  Because of the small quantities of boards and the diversity of the design, panelizing them turns out to save quite a bit of money.  I’m currently running 2 of the main stack plus the first board of the controller.  If I ordered PCBs separately, it’d run about $1500.  Panelized, they came in under $600.  Assembly for each of the jobs separately would run around $3300 based on mostly-accurate numbers, but the panel drops that to around $2200.  Overall I’m saving around $2000 by panelizing.

The downside is that it’s a rather complicated process.  I’ve worked for the last week trying to get everything in order so EpecTec and Screaming Circuits don’t end up with major problems because of what I send them…  However, once it’s figured out the first time, I can do subsequent panelized runs with a lot less effort.  And thanks to the wonders of Open Source, I’m hoping others out there will be able to do the same because of the scripts I’m writing.

I’m going to see if I can make enough time in the next few days to note down most of the issues I’ve run into, and hopefully save others some trouble in doing so.  First up will be setting up the PCBs and panelizing them.