I talked about soldering small surface mount LED in my previous posts by using DIY reflow oven. Today I would like to show you how to rework similar LED, which is, to desolder this LED off the PCB and solder a new one on it… continue on yu.xueming.org
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The first impression of the Ricoh Theta 360 Degree Spherical Panorama Camera is its odd appearance — to me it feels like a bar of chocolate wafer. The dual lens reminds me of the bubble eye goldfish. For some reason I was given this 1st generation Ricoh Theta camera for free, but broken. So why not taking a peak at its inside? … continue on yu.xueming.org
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A recent project requires soldering 600+ tiny LEDs on long narrow circuit boards. The LED, Philips Rebel Z ES, is as small as 1.6mm x 2mm, and is placed 2.5mm apart from each other…continue on yu.xueming.org.
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I am working on a DIY PCB project that requires mounting three PICOR PI3301 Power regulators. Unfortunately, the PI3301 comes with a high density 123-pin LGA footprint in a 10mm x 14mm package… continue on yu.xueming.org.
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The “copper to drill hole” distance is an important rule for circuit board design, just like the “copper to copper” clearance… continue onyu.xueming.org
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First of all, let’s take a look at the video clip below (link) to find out how it is possible to reflow solder components without stencils.
I talked about DIY your own reflow oven in my previous article. People may wonder that only a functioning reflow oven won’t do the job as you must have stencil to dispense solder paste. Yes, stencils are usually considered as key piece of equipments for reflow soldering process. The purpose of stencil is to restrain the solder paste within the specific pad area. The thickness of stencil also decides the amount of the paste to apply for soldering. Stencil, however, is non-trivial to manufacture. It usually requires special material and laser-cutting. That’s why stencil is quite costly, sometimes even more expensive than your PCB board.
Figure 1. Left: Solder paste applied with stencil; Right: Solder paste applied manually (without stencil)
The difference is quite obvious: you get a clean and neat solder paste dispensing with the help of stencil. On the contrary, the PCB on the right side looks messy as the paste is simply dropped on to the pads without a stencil. Messiness might be acceptable considering this is not your final product. The “bridge” where paste (usually applied too much) connects to its neighbors across different pads seems to be a problem because it might cause short-circuit.
Figure 2. The sketch illustrates how paste is bridging across two pads.
With the help of “surface tension”, the PCB on the right side of figure 1, however, is still a useful board for reflow process. As we know when solder paste is heated to certain temperature, it melts and becomes “liquid”, which will flow in compliance with surface tension. The molten solder that was placed in between pads (also called solder mask) will be pulled away by its neighboring paste that was placed right on the pads. Further more, surface tension also helps the alignment of components. If a component is not accurately positioned over its footprint, the surface tension will help “move” it into place when the solder paste melts. The video above contains a clip towards the end shows how small SMT LEDs are “pushed” and “rotated” into place when the solder paste melts.
So, as long as you have a reflow oven, chances are that you can start soldering your small footprint ICs without stencils or automatic mounting machines!
Although I can skillfully solder as small as 0.5mm pitch QFN package chip by hand (post, video), more and more space saving components appearing on the market are totally IMPOSSIBLE to hand solder… continue on yu.xueming.org
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I sent out a new circuit board design to a PCB fab house last week, but was put on hold multiple times for the reason of “insufficient copper to copper spacing”. I have been using the same PCB fab for quite a long time, and I’m quire sure that the design was correct, at least my EDA software (Altium Design) didn’t report any error when running the DRC (design rule check). In order to triple check that my design meets the fab’s mini trace/space capability (6mil), I even increased the minimum clearance rule from 6mil to 6.1mil, which, of course, was a nightmare as I had to go through all the wiring again. It drove me nuts when I was put on hold again for the same reason, which really confused me.
The CAM engineer told me there were more than 50 instances of copper to copper spacing less than their requirement (6mil), most of which read something like 5.5 mil or 5.7mil. The single decimal place of those numbers seems very suspicious — was the gerber file accurate enough? After going over all the parameters regarding fabrication file export, I finally figured out why:
After your PCB design is finished, you choose “File” -> “Fabrication Outputs” -> “Gerber files” to launch the CAM conversion setup. The first tab of the diagram contains the accuracy setup “Format”. As is explained, “2:3″ gives 1mil resolution,”2:4” is 0.1mil and “2:5” is 0.01mil. Apparently, if you choose “2:3” for gerber export, the decimal part of all your coordinates will be trimmed to 1mil resolution. This also means all your design is virtually moved a little bit because of the trimming, and you have no idea how the trimming is calculated, whether intelligently or not. For sure this is going to break your restraint regarding trace spacing.
However, “Gerber Setup” is not actually generating your gerber files. Instead, it converts your design to CAMtastic (.cam) file. You can think of CAMtastic as some sort of filming process, in which all your trace/silkscreeen/drill holes are retained with netlist/relationship being removed. Now you need to output layers in your CAM file respectively, which usually contains the final format the fab house takes. Then, here comes another dialog, and this is exactly where I got screwed:
In your CAMtastic window, go to “Export” -> “Gerber”, the following windows pops up:
Pay attention to the “Format” again, this is very last setup that is really going to affect your output resolution. The one I mentioned before was the resolution for CAM, and this one is for the gerber file. Make sure you choose as high resolution as you want since the default seems to be “2:3”, which caused my design failing the PCB house’s sanity test.
This time, the higher resolution export went through all the PCB houses’ process smoothly without any problem. But I still didn’t quite get it — why all my previous designs worked well in spite of my unawareness of the resolution issue? Later on, I realized all my previous PCBs were designed on a 1mil or coarser grid. This time, however, the board was so dense and I still wanted to keep the cost low on a 6mil fab. So I lowered the grid to 0.05mil. And here comes all the trouble! As it is already warned me on the first dialog: “The 2:4 and 2:5 formats only need to be chosen if there are objects on a grid finer than 1 mil.”
For lab geeks or hobbyist who often sends out small quantity PCB fab orders but doesn’t care about a little bit extra work, this post will help save a decent amount of money on PCB manufacture cost… continue on yu.xueming.org
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This is a quite interesting project which requires digging out the 3D stereo camera module from the LG thrill P925 smart phone and driving it somewhere outside the smart phone. What… continue on yu.xueming.org
Update: my blog has moved! Check out yu.xueming.org
Xueming Yu 