[time-nuts] Parts Selection - Short Run Assembly

[Bob Camp]

Hi

There are machines out there that are essentially robotic syringes. Several outfits make them. They can also be used to put down adhesive. I don't know of anybody who actually likes them.

Best bet - get / make a simple screen printer. A manual one is going to be cheap. A home made one is even cheaper. The solder screen it's self won't cost you much more than the time you would spend programming the robot and messing with it. Solder screen / stencil generation is a "push button" sort of thing with a modern pcb layout program. 

Bob


On Mar 26, 2011, at 8:40 AM, shalimr9 at gmail.com wrote:

> 0.5 mm TSSOP, MSOP and QFPs are not fun but OK. 0.65 is considerably easier, not only to assemble, but also if you have to put a scope probe tip on one of the pins. I can work with 0.65 without magnifier, 0.5 I can't. 
> QFNs are a no-no for me in the current state of affairs, even though I see the day coming soon where I will have to get equipped just because there are interesting parts only available in QFN packages.
> 
> 0805 parts are also OK, smaller probably not if I have a choice. I understand that with microwave circuits, you sometimes have to use smaller packages to match line width. That sucks.
> 
> I just finished building a couple of prototypes with 0805 passives, SOIC and MSOP and 0.65 QFPs (about 120 parts total each board) and while it does not look very good, both worked the first time. I had to do it myself because my assembler was not available and I needed to check these protos. The assembler will build the next 10. It took me about 4 hours to build 2 boards. I used a fine tip, temperature controlled soldering iron and a magnifier mounted on a old pair of recycled sunglasses :)
> 
> I am now seriously looking at a hot air rework station and an oven because that's just the only way forward.
> 
> If someone can recommend a solder paste dispenser that works better than a seringe, I would be interested.
> 
> Didier KO4BB
> 
> 
> Sent from my BlackBerry Wireless thingy while I do other things...
> 
> -----Original Message-----
> From: "Bob Camp" <lists at rtty.us>
> Sender: time-nuts-bounces at febo.com
> Date: Fri, 25 Mar 2011 13:07:32 
> To: 'Discussion of precise time and frequency measurement'<time-nuts at febo.com>
> Reply-To: Discussion of precise time and frequency measurement
> 	<time-nuts at febo.com>
> Subject: [time-nuts] Parts Selection
> 
> Hi
> 
> 
> 
> Just a show of hands sort of thing. It comes up each time we talk about
> projects and never really gets answered. Rather than trying to work it out
> as a part of a project, let's see if it can be addressed by it's self. 
> 
> 
> 
> How many people are willing to solder up a project with multiple 0.5mm
> spacing >=144 pin package IC's on it? There's a typical package drawing at
> the end of: 
> 
> 
> 
> http://www.national.com/ds/DP/DP83816EX.pdf
> 
> 
> 
> I'm sure it's a "what's in it for me?" sort of question. Let's assume it's
> just neat piece of bench gear rather than a home grown cesium standard for
> $100. 
> 
> 
> 
> I don't think this part really matters, but it might to some people. Say
> each chip is well below $100, but above $20 each. There might be only one
> part like this on some projects, but for the sake of this poll, let's say
> there are two or three of them. Net is roughly 250 to 500 pins like this to
> solder, on some number of packages. It's part of a project that will cost
> you $250 to $500. 
> 
> 
> 
> I'm not talking about opinions on weather it can or can't be done. It
> certainly can be done and is done every day. What I'm asking is - would you
> buy a bag with the parts all in it? If you do are you going to put it
> together in a reasonable amount of time?  Reasonable time might mean
> different things to different people. For the sake of completeness, yes you
> also need to get it working after you assemble it. 
> 
> 
> 
> Next layer (you knew there had to be more) - have you done it before
> (anywhere)? / done it in the last 2 years (at home)? / are you set up to do
> it today (at home)?
> 
> 
> 
> I'm not trying to get into "how would you do it / what would you need /
> could you farm it out". Those are also neat questions, but not part of this.
> 
> 
> 
> 
> I'll start off the voting (and yes the answers are out of order):
> 
> 
> 
> Done it in the before - yes.
> 
> 
> 
> Done it in the basement / last 2 years - no. 
> 
> 
> 
> Set up to do it in the basement - yes, but not set up well. 
> 
> 
> 
> Would I buy one - done that before. Likely would again. (counts as a yes).
> 
> 
> 
> Would actually do it in a reasonable amount of time - unlikely.  (That
> counts as a no).
> 
> 
> 
> Any more votes?
> 
> 
> 
> 
> 
> Bob
> 
> 
> 
> 
> 
> 
> 
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