8-pin SOICs viable in kit?

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cstratton
 
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Joined: Wed Sep 29, 2010 3:52 pm

8-pin SOICs viable in kit?

Post by cstratton »

I'm prototyping a fun project that I think could have real potential as a kit. It consists of 3 8-pin ICs, and about 12 passives.

The catch is that two of the ICs do not come in packages larger than an SOIC-8, the third is available in either that or a dip.

Personally, I find SOIC packages fairly easy to solder, and at 8 pins you only have two interior pins on each side, so the chances of cascading difficulties are limited. An occasional solder bridge is to be expected, but that's easily cleaned up with braid. I have a lot of temptation to market this as an opportunity to try some "relatively easy" surface mount, and perhaps do at least the resistors in 0805 or even 1206 as well.

But perhaps many will consider that a deal breaker. I could do partial kits with the surface mount ICs already installed, but at that point it's not that much more work to pre-assemble the entire thing, at least if the passives are SMT too. For the primary application there is some mechanical fabrication and integration that could be left to the "builder" though.

I've intended the board to be re-purposable and customizable - it can stack on top of the corner of an arduino using just one of the shield connectors and be be reprogrammed/reloaded with an extended version of the arduino isp sketch. Still, I assume I should be programming the two flash parts ahead of time, so an arduino is not required. It looks like SOIC-8 sockets are about $16, so I should be able to do this either to bare chips or with pogo pins to points on the board if the SOIC's are pre-assembled.

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brucef
 
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Re: 8-pin SOICs viable in kit?

Post by brucef »

Just one occasional kit builder's opinion here... I'd like to get into surface mount electronics, or at least give it a low-commitment taste. I don't expect surface mount work to be as easy as through hole, but I wouldn't want to start with some hundred-pin QFP. No idea what your kit actually is, but it sounds to me like you've got something that, in technique at least, would be attractive to someone like myself.

YMMV, plural of anecdote is not data, etc, etc.

If you go that route, it may be helpful if you could list and even possibly sell as options any small bits a through-holer might need to make the transition easier, e.g. braid and suitable tweezers.

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cstratton
 
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Re: 8-pin SOICs viable in kit?

Post by cstratton »

Bruce, good to hear that someone finds the "intro to surface mount" idea plausible. As far as tools are concerned, when I stuffed the first PCB for the new prototype version this afternoon, what I used was

* radio shack 15 watt iron (with a moderately newish tip)
* dollar store tweezers
* chipquick lead free tin/silver silver solder from digikey (I should use the radio shack version next time to verify it)
* messy flux from radio shack on a qtip

I didn't end up needing any braid this time, though I could look at the economics of including some, since the narrow stuff could be preferable to the wide version available at radio shack.

I'm leaning towards doing most of the resistors in 0805 surface mount as well, except for one that sets the audio gain which people may want to be able to change for a different value more easily. This will probably necessitate including a several spares, because they do get lost, but they are pretty easy to solder - just tin the pad with iron in dominant hand and solder in the other, put down the solder, pick up the resistor with tweezers and solder that end, then trade tweezers for solder again and do the other end. Honestly, the hardest part is trying to flip them over if you get one upside down on your desk - for some reason, every time you drop them off the tweezers they seem to land upside down again! The IC's go pretty much the same way, except that you do one corner, check alignment, then do the opposite corner.

rellik
 
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Re: 8-pin SOICs viable in kit?

Post by rellik »

Like Bruce, I'd be interested in a intro-to-SMD kit (just my 2 cents).

bigmessowires
 
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Re: 8-pin SOICs viable in kit?

Post by bigmessowires »

One more opinion: I'd say that whether the SOIC-8 is actually easy or difficult to solder is not relevant. What matters is whether a sizable chunk of your potential customers will be scared away by the perceived difficulty of SMD soldering. You know your audience better than anyone, but for the general hobbyist community I think there's a pretty widespread fear of SMD work, so you would very likely lose some customers.

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cstratton
 
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Re: 8-pin SOICs viable in kit?

Post by cstratton »

At this point, my primary target would be those who think they might like to try some easier SMD. The kit will probably be in the range where people can buy it to take a chance on, though I've given some though to coming up with something even simpler/cheaper as an SMD "nibble"

For those who really don't want to deal with SMD at all, I've ordered a test version of the board revised to all through hole passives, thinking perhaps I could offer that with the SMD ICs already installed for about five bucks more. This would leave the builder to solder an 8 pin DIP (socket), the through hole passives, and mechanically integrate the finished result - so it will still feel like a kit.

TheFallen
 
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Re: 8-pin SOICs viable in kit?

Post by TheFallen »

Could you not put in pads/packages for both SMD and through hole, It'd be easy to include both types of passive components. That way you can semi-guarantee a working circuit at the end of their efforts, regardless of any SMD mistakes.

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cstratton
 
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Re: 8-pin SOICs viable in kit?

Post by cstratton »

TheFallen wrote:Could you not put in pads/packages for both SMD and through hole, It'd be easy to include both types of passive components. That way you can semi-guarantee a working circuit at the end of their efforts, regardless of any SMD mistakes.
That was actually my original plan, but when I went to do it I discovered it just wouldn't fit. The entire board is only one inch square. Even with just the through hole parts by themselves, there's not enough room to silkscreen legible reference designators for everything, so the instructions for that version are based on 3x magnified pictures showing where to put each component.

minerva
 
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Re: 8-pin SOICs viable in kit?

Post by minerva »

The fact is, you cannot realistically make interesting, useful, powerful modern electronics projects if you're completely opposed to using any surface mount. Giving an electronics designer a "no surface mount" dogma is just so crippling to the usefulness and flexibility of the finished design.

8-pin SOIC is pretty easy to solder.

I think, personally, that 8-pin SOIC and SOT-223 voltage regulators are two of the best SMD packages to give to SMD beginners as relatively easy to handle, easy to solder packages, to get them into soldering SMDs and get them over the BANNED barrier that "I can't do SMD, it's too hard".

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