Low MOSFET IDSS current

But FIT-bashing is way more fun. ;)

I've had one or two more-or-less bad batches of stuff, e.g. a reel of JFETs that were 2 dB noisier than the ones another reel, but in general I don't buy enough parts to test to 0.1% AQL even if I had the inclination.

And lots of parts are likely to be damaged during test--back in the day, JAN TX screened transistors were notoriously less reliable than the COTS ones due to all the extra handling.

IME parts die due to maltreatment, not quality problems. Now if I were making car air bag controllers, I'd worry more about that sort of stuff, but for us, if it passes final test, it's OK.

Cheers

Phil Hobbs

What's wrong with AQL on reels?

Bad handling procedures from long ago, and less reliable designs. This can kill parts during assembly. Modern parts and procedures should be a lot more reliable.

We are not talking about failures or design problems. We are talking about incoming inspection.

If it passes final test, how do you know how close it is to failing?

Maybe your quantities are not high enough to warrant AQL, but others may need it.

See 6.2. Test Product for Acceptability: Lot Acceptance Sampling

This section describes how to make decisions on a lot-by-lot basis whether to accept a lot as likely to meet requirements or reject the lot as likely to have too many defective units.

This section consists of the following topics.

What is Acceptance Sampling? What kinds of Lot Acceptance Sampling Plans (LASPs) are there? How do you Choose a Single Sampling Plan? Choosing a Sampling Plan: MIL Standard 105D Choosing a Sampling Plan with a given OC Curve What is Double Sampling? What is Multiple Sampling? What is a Sequential Sampling Plan? What is Skip Lot Sampling?

Other excellent references on the web.

Maybe. But the sheer amount of fixturing and labour involved in testing every kind of part that we use would make the whole thing uneconomic. Parts are cheap, but labour is expensive, and fixtures take up a lot of space.

How would AQL help me know that? Reliability vs. quality again.

I'm sure that's true. Joh's talking about low volumes, and I'm talking about really low volumes, so far.

Cheers

Phil Hobbs

That's sounding like the quality-control ritual blather.

What exactly do YOU DO when you get that reel of caps?

I've been thinking about that. An automated tester shouldn't be very complicated. Separate jigs for diferent size smd's. A little stepper to advance the reel to the next component. A fast precision LCR meter to measure the components. 0.1% should be good enough for most parts.

Perhaps a small Teensy or Arduino to log the measurements and step the reel. Some of the guys on Hackaday do fantastic work on small mechanisms.

One problem is to find a way to mark bad components. If the test is fast enough, maybe test the whole reel. 3600 parts at 100ms per part would only take 6 minutes.

You set the limits for the test. Parts that are outside the limits are rejected and not installed.

Hopefully that will change.

The math is real. A lot of companies depend on it.

That's what I am setting up now. I am leaning towards automated testing and logging the results. A simple reel tester shouldn't cost much to make, and could be very fast.

I have found if you do not specify the incoming test, companies will ship you the dregs that failed AQL at other companies. As an example, I have received 16 pin HC7474 through hole parts. They were marked 74HC7474, but I don't know of any 16 pin versions. Obviously someone rejected them, so they sent them to us.

I was hoping some mfg guys would chime in and tell us their horror stories.

sting

I'm sure they do, but my shop is about 1100 square feet and 2-1/2 people, a nd there's only so much mojo to go round. The cost of the equipment is a ni t by comparison with labour and (especially) opportunity cost.

Plus we'd have to put those parts back into reels after testing, and all fo r (very probably) no benefit.

No thanks.

Cheers

Phil Hobbs

'Companies'? What company was that, something from Knockturn Alley or eBay?

I've never received anything but good parts from the leading distributors.

Sixteen-pin 74HC74s, forsooth.

Cheers

Phil Hobbs

All hat and no horse.

Marked 74HC7474? That's funny. I guess on a 16-pin part, there's more room for text.

Buy from authorized distributors. Real 74HC74s are so cheap, there's no reason to buy from counterfeiters. Or to do receiving testing.

You will need more space when you go to high volume.

Why remove the parts for testing? Use heated shaft to punch two holes through the top cover tape. At the next station, insert two kelvin leads to measure the component.

You could also cut the tape after measuring to kit for assembly.

I forget. It was a while ago, before ebay. The only suppliers were the big national brands, and we only bought from them. But they screwed up a lot.

I'm sure. But there's always human error, especially when you go to higher volume.

l.com:

testing

and there's only so much mojo to go round. The cost of the equipment is a nit by comparison with labour and (especially) opportunity cost.

for (very probably) no benefit.

afaiu at one of the places we get stuff assembled the pnp machine measures components on the way from tape to pcb

though I have no idea if it is just a coarse measurement to check direction of diodes and rough value of resistors and capacitors

Of course, we only buy from authorized distributors. No ebay or surplus houses.

If you don't do incoming inspection, how do you know they haven't sent you parts that failed AQL at some other company?

If you don't do AQL, how do you know the distribution of the parts?

It seems you are taking a lot for granted. I'm not so trusting.

Especially when I think it might be able to test a whole reel, perhaps in under ten minutes including setup.

I've been in reasonable volume production before. You have no time when it hits to do a proper job, and you spend a great deal of time reccovering from mistakes and bad or wrong parts.

The time to solve these problems is right at the beginning.

You have excellent stock inventory programs. These are invaluable, and must have taken time to write and debug. You know where you get the parts, how much they cost, and how many you have used.

But you have no idea if the parts actually meet spec, or what you are putting in your product.

Yah, I could do a lot of other unproductive things too. But I could also spent the time designing new stuff, which is way more fun and way more lucrative than picking largely theoretical nits in production.

Cheers

Phil Hobbs

houses.

An *authorized distributor* sent you 16-pin DIPs marked '74HC7474'?

Do tell.

Cheers

Phil Hobbs

No serious distributor would do that. They would lose their principals ASAP.

And no parts would fail someone's incoming inspection without the manufacturer knowing about it.

If you divert your energy into sidetracks like this, you won't survive. Put your energy into designing and selling and supporting products. In the very rare case that you have a part problem, fix it.

If you don't ship, you will never have quality problems.

We check one or two parts on each received reel to see if they are the right value. We have a machine-vision thing that inspects built boards for soldering, part number, orientation, all that. After all, you could pick a part from a reel and put it in the wrong place, or backwards, or something.

Our auto P+P does inspection during placement.

We inspect and test every production unit extensively. Bad parts will show up there, and occasionally they do.

We trust a bunch of suppliers to do things right. *They* test every part.

Really, we are professionals, building and shipping in volume. Our field reliability is superb. We get awards. I don't think you have standing to lecture us on this.

Unlikely. This time of day, it would be gin and tonic.