X5R vs X7R MLCC

I can sometimes see some ringing on a TDR, and reflections that are obviously off the edges of the board. But a copper plane is pretty lossy as a transmission line, and not terribly interesting.

That looks about like a 1-ohm resistor to the initial step, then becomes a capacitance after the wave hits the edges of the board.

There are a zillion theories about bypassing, and almost all of them work. I knew a guy who didn't believe in using bypass caps on multilayer boards, and he was right too.

int was that when you can't, the options are especially wide for decoupling caps. Even more so if you've added a few extra pads so aren't relying on a ny one cap to provide enough capacity every time. I use/specify salvaged pa rts routinely to keep BOM rock bottom.

p of tea, but that's where I operate. When specs can be vague at best it's the ultimate way to minimise BOM. They're big business in China, key to kee ping consumer product costs down.

You can buy what you want. Tested, untested, anything. Parts relabelled as something else are also popular, I've no time for that game. Tell them what you spend on parts, tell them exactly what you will & won't accept & make it plain that if a single batch ever fails to meet that they will never get your business again. Also say if not in stock now don't worry, will buy so mething else soon. Include that letter with every single order in case a su bordinate doesn't know or they get greedy.

Yup. I have to be cheap.

NT

Makes sense. Smaller boards are cheaper but that's obviously not as important to you as standardization. We're at the opposite end of the spectrum. If every sq.cm. isn't used, the board and the case was too big.

I didn't mean BGAs on the bottom. That can be problematic. I meant decoupling on the backside of the BGA. Sometimes we reclaim the space on the back side for something else, too (blind and buried vias).

Perhaps you don't worry about it but we sure do. Temperature => failure. We're often pushing the temperature envelope and electrolytics don't like it at all.

I knew a guy like that too. One day he had no caps on his board and it didn't work. When I saw his waveforms and ground bounce, I told him all about decoupling. The next day his board was working perfectly. He also had in excess of 100 caps on it (~4"x6" board) - mostly tantalums. =:-|

I got started as a hobbyist when I was 10. My older brother was interested in electronics, and I thought that was interesting. Building circuits out of books was fun, but the parts were way too expensive--it took my whole week's allowance to buy a JW Miller loopstick for a crystal radio. (No, I didn't have a paper route. They had gone away by then and anyway I was way too lazy.) ;)

It took several years before I could actually design things that worked, which made me _nuts_. With a hobby background and a bachelor's in physics and astronomy, I was well enough equipped as an EE to do reasonably advanced design of satcom equipment when I graduated.

Perhaps I'm biased, but IME folks with early hobby backgrounds make the best designers.

Cheers

Phil Hobbs

I had a paper route, so had cash. ...and a great electronics store to spend the cash in (and the newspaper was innumerate, leaving me a larger than normal share). ;-)

But which is the cause? Does an early hobby background make the best designer or does interest/aptitude make both. Hobbies don't just appear out of the air.

I don't believe it's possible to learn even basic competence if you ignore either one of theory & practice. When students sit in lectures hearing abou t circuits they fail to relate it to things they know, and fail to grasp mu ch of what's being said, and forget it soon after. It's just not an approac h that works at all well.

NT

int was that when you can't, the options are especially wide for decoupling caps. Even more so if you've added a few extra pads so aren't relying on a ny one cap to provide enough capacity every time. I use/specify salvaged pa rts routinely to keep BOM rock bottom.

p of tea, but that's where I operate. When specs can be vague at best it's the ultimate way to minimise BOM. They're big business in China, key to kee ping consumer product costs down.

Reels & bagged loose are the default options. There are loads of places sel ling such stuff in China.

When a board has more decoupling caps than essential, it doesn't matter if the odd one is below spec. When your board is conservative on tr specs you can fit any of 100s of types, it doesn't matter, only the basics need match . If you look in some consumer products you'll find parts that aren't even marked. More popular is relabelled parts so they look new.

NT

Yet it seems that's the norm.

And the difference really shows. I started when I was 6. Doing all the nutty electronic things people say you can't do is another way to learn.

NT

I admit that I've never worked in this end of the business (didn't even know it existed) but is scares the crap outta me.

Unless it's shorted, which is the favored failure mode for MLCCs.

Most passives aren't critical, agreed. ...unless they're open/shorted.

Some by contract. Some obviously removed. House numbering is also common.

That is really scary. Now I'll have nightmares. ;-)

re either one of theory & practice. When students sit in lectures hearing a bout circuits they fail to relate it to things they know, and fail to grasp much of what's being said, and forget it soon after. It's just not an appr oach that works at all well.

It always struck me that the education system is in the hands of the incomp etent. Schools especially need a total overhaul from top to bottom.

NT

point was that when you can't, the options are especially wide for decoupl ing caps. Even more so if you've added a few extra pads so aren't relying o n any one cap to provide enough capacity every time. I use/specify salvaged parts routinely to keep BOM rock bottom.

cup of tea, but that's where I operate. When specs can be vague at best it 's the ultimate way to minimise BOM. They're big business in China, key to keeping consumer product costs down.

selling such stuff in China.

It's just engineering really, taking cheap parts & making the resulting pro ducts work well. I started at the other end of the scale & always disliked the gross inefficiency. It got me thinking how to minimise costs.

if the odd one is below spec.

Some salvaged parts are better than others. No-one should use just anything .

ypes, it doesn't matter, only the basics need match.

n marked.

some yes

They're very common. I don't like them one bit as often some of the chips a re plainly something else entirely. Or some functions work some don't.

If you get a reel of chips with various random date codes you know what's g oing on. Mfrs don't mix reels like that.

NT

John Larkin wrote

That is nice, a picture is worth a thousand words.

are

t.

ng.

nore either one of theory & practice. When students sit in lectures hearing about circuits they fail to relate it to things they know, and fail to gra sp much of what's being said, and forget it soon after. It's just not an ap proach that works at all well.

It's a possible failure mode. The education system tests how much students remember with practical tests, and employers do have a reasonable expectati on that the students will be able to apply what they have learned in practi ce.

The higher education system is more about teaching students how to look at problems and work out potential solutions, how find out what they need to k now from textbooks the published literature.

People working in a specific area can't expect that the education system wi ll teach every student all they need to know about that area - the kids are n't programmed as special purpose computers.

Krw is silly enough to believe anything.

mpetent. Schools especially need a total overhaul from top to bottom.

And NT is silly enough to take his opinions seriously. NT's antiquated data base does need a total overhaul from top to bottom, but it's probably as i mmune from revision as krw's is.

Things might have gotten worse but my father (an EE prof) complained of the exact same things in the '50s.

OK, you've got my curiosity piqued. How many widgets do you manufacture (single run)? What sort of complexity? I can't imagine taking a pile of unknown parts, putting them together on a board, and having it do anything like what it was designed to do.

Sitting and listening to a lecture is just the first step in becoming a useful EE. Necessary but not sufficient.

Class projects should complement the theory, but lately they are mostly playing with those Arduino things. Again, the universities' theme is maximum tuition and minimal actual expense.

Was your dad a salaried, tenured professor? That's getting rare now too.

Some math-y type could tell us what is the impedance of an infinite plane straddled by two ground planes, with a launch connector at some point, like in my pic. Is it pure ohmic forever?

My initial 1-ohm region might be flat or might be sloping down. That