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Topic: Quick teardown of a "Samurai Watch" (Read 3907 times) previous topic - next topic

Quick teardown of a "Samurai Watch"

I couldn't resist the impulse to get one of the $3 Samurai LED Watches when I saw it the first time.  They can be found both at ebay and other local shopping sites.

I'll probably never wear the watch for real, but I wanted to take it apart so see how it was made.

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The square back was easy to just snap off with a small screwdriver.

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Revealing a single CR2016 battery and a pcb hidden beneath a piece of protecting plastic.

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To be continued.....

Re: Quick teardown of a "Samurai Watch"

Reply #1
Flipping over the guts reveals something that could be four 7-segment displays under a piece of sticky plastic tape.

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The segments lights up rather uniformly, probably thanks to the thickness of the tape.

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Peeling off the rather thick plastic reveals..... nothing....  or at least just an empty pcb under the black grid.  Intriguing.... are the leds hidden there under?

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After removing the black plastic thingie it seems like there are no leds there either???

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The back is not too exciting though.  A tiny 32khz crystal and a chip under a black blob as in so many other cheap electronics.

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To be continued....

Re: Quick teardown of a "Samurai Watch"

Reply #2
Of course there are leds on the pcb, but it puzzled me for while - at least until I ran my fingers over the pcb. (In my defense I must say that it was kinda dark in the room and my eyesight is not what it was 25 years ago.)

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The leds are there.  Mounted as bare dies on the edge of the smd pad and then connected with a bonding wire over to the other pad! I've probably ruined a few of the bonding wires with my finger, but it was worth it because this is the first time I've seen bare/naked led dies connected to a pcb.

Well...  That's it.  This was more of a photo album than a proper teardown, but I really don't care :-)  Just wanted to share it with you guys (and gals if there are any here).

Re: Quick teardown of a "Samurai Watch"

Reply #3
If you take apart the led display of a cheap alarm clock they have leds on the pcb like this, too.

Re: Quick teardown of a "Samurai Watch"

Reply #4
Interesting.  I wonder how much cheaper it is to put the dies on the pcb instead of regular 0603 leds?  The assembly plant must have access to specialized equipment to do the placement of the tiiiiiiiny die and the bonding machine.  That's not something any shop have....

Re: Quick teardown of a "Samurai Watch"

Reply #5
Packaging is rather expensive, so they probably save a lot by using bare dies. My guess would be that for a simple semiconductor like an LED the packaging is more expensive than the actual die. Bunnie posted an article on what Chinese workers achieve with bamboo tweezers and a steady hand. Bonding does not seem to be that much of an issue after all.