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The cheapest and really only available package for the accelerometers is LG-14 which is the package used for the MMA7331LT accelerometer that jinx is going to use. This acceleromter is really inexpensive at only $2.32 a pop, but the package is very difficult to deal with. I bought two of them, the first one shot out of my tweezers and was lost forever, the second one met its demise by what happens in the rest of this document.

Let me start off by saying if you want to use this then I’ve found a way to do it pretty easily. First use the artwork originally created in this post by its author.  It is also in the gallery for this post. Then use this instructables method or you can watch this video. Basically you HAVE TO use a diy home reflow soldering method. Basically you get solder paste (like glue) put it on the chip and board then put it in a toaster oven timing everything carefully.

If you dont want to do it that way you can put the chip upside down on the board with a little glue to hold it in place, then you can solder really small wires from the chip to the pads. Afterwords just use resin or expoxy and coat the whole thing so it is sturdy. The main pain in the neck with this method is that everything is upside down so you have to be extra careful with the pinning, and since its a accelerometer your axises will be off.

I tried to do it by just soldering and using a small butane torch. I dont think it worked. When I tested it it seems to output something but i’m not sure if its working or not. I have no confidence in the adapter and I dont want to use it in my design. I will use the footprint and all the stuff I made in the main board for jinx and will use the diy reflow process when I find a toaster oven ( and get more accelerometers ). This way its on the board and does not take up a lot of space. So, the adapter is out the window.

But someone else might want an adapter so I’ll post all this stuff here. I didn’t just make it a straight adapter, I added all the caps to it and only used the pins that are really connected to something. Only 8 pins are used on the 14 pin lga ic. So if you wanted to make an adapter you could use this circuit and just be sure to use the diy reflow process when you actually “solder” the ic to the board.

I used the laser printer method for transfering the design to the pcb. Be sure to print out the “reverse” when you print it from ultiboard. NOTE: if you use my ultiboard design remove all the NC pins connections to ground, you can connect them to each other but I dont recommend you connect them to ground.

So, basically print the circuit (in reverse) on some magazine paper and then heat it up on your board with a iron. Once you start to see/feel the traces coming through your paper (or it just feels right) take your board up and put it in some warm water, let it soak for about 20min. Then go and rub off the paper the toner should remain attached to the board.

It comes out pretty crappy, or at least it does for me so get a exacto knife and a ultra fine tip (black) sharpie and fix it up.

Now you can etch it. There is a really cheep etchant on ebay it comes in a powder and makes tons of etchant. I just put two spoonfuls in about .5c of water for this one.

I had to let it sit for about 2+ hours when I noticed it started to remove the copper I agitated it a little with a plastic fork.

Then when its finished take it out and clean it off. You dont want to leave it in for too long after it has etched the exposed copper because it will start to eat away at the unexposed copper too! Genty scrub off all the black toner/marker with basically anything abrasive.

Again get out your exacto knife and make sure the smaller lines are not connected, especially the ones going into the lga-14. Then you can drill the holes, for this you really need a drill press. I use a dremel with a drill press, but then you run into another problem, the drill bits are so small they dont fit in the dremel. I fixed this by adding masking tape around the bit then tightening it a lot. Make sure your bit is not wobboling before you start to drill, and wear saftey glasses.

And of course from there everything was already wrong because I was unsure if the connections had been made to the chip. Its impossible to tell because there is no place to connect to to test for connection. Once I get new chips and a toaster oven (or i could use the skillet method) I’ll do it again but it wont be on this adapter board it will be on the main jinx board. But some of you might want an adapter like this so if you do go ahead and use the files I provide (maybe just as a starting point).

AccelAdapter (multisim and ultiboard files)

1. ZoneMikel's Blog » Blog Archive » JINX 555 timer 40kHz Oscillator for Sonar says:

   May 17, 2010 at 1:34 pm

   [...] Well after a few days (and getting my soic 555’s) I decided to test this. I created a circuit to test it in multsim, then ultiboard then I etched it using the process described in my other post [...]