Jumper to replace Inductor

1206 on its side? That'll confuse them.

Cheers

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Syd

On Thu, 30 Jun 2016 11:26:41 -0400, rickman Gave us:

A test point. Typically Silver Plated Copper or Tin plated Copper, but more often Silver as it takes solder better.

On Thu, 30 Jun 2016 14:27:53 -0400, DecadentLinuxUserNumeroUno Gave us:

So, you are ignoring the test point suggestion?

Any time you need to replace a part already laid out with a jumper, you can use a test point.

Two benefits...

A: It is usually cheaper than a zero ohm resistor of the same form factor, and

B: They are available of tape and reel and are pick and place compatible if you get the right type.

Three if you count the fact that you can also actually use it as a test point.

Usually you can use a plain resistor ahead of a linear regulator, just pick whatever resistance won't cause problems anywhere.

NT

I'm not sure what you are picturing. The original board was designed to work with an FPGA which was available in two versions, 3.3 volts everywhere or a 1.2 volt core. The (optional) 1.2 volt power converter chip was a buck switcher with an inductor on the output. I want to use a linear regulator instead so there won't be any new issues with EMI. Given this we may skirt by without redoing EMI testing. The only problem with this is the inductor footprint does not suit any resistor size without crowding nearby vias, reducing the clearance to around 7-8 mils. The assembly house may or may not have an issue with this, we'll see.

I'm just looking for something that mechanically fits the pads and provides a short. 1206 is the closest fit I can find so far. A 1205 or better, 1104 would be perfect, but they don't exist. I thought I found a jumper that fits, but I was reading the specs wrong and it is too long. A piece of bus wire would be great, but I don't think you can pick and place them, lol.

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Rick C

You could just use a super-low value inductor, same size.

0.47uH? Check for stability, of course, but I'd think most regulators wouldn't mind it. As far as they could see the load would still be massively capacitive at frequencies that matter.

Cheers, James Arthur

THINK! An assembly house can't auto pick and place that as the vacuum nozzle can't pick it up by its side! Problem totally not solved...

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Rick C

On Thu, 30 Jun 2016 21:14:16 -0800, Robert Baer Gave us:

"Tombstoning" a part requires hand assembly operations.

Automated assembly methods do not perform that way. THINK!

THINK! Use an 1206 0-ohm resistor and place it in its side; "problem" solved.

maybe with the right furniture the P&P can drop the chip flat and then pick it up sideways.

| | -----___ | \ | \ | | | | | |_______|

################ ################ ################ |################ | -----___ | \ | \ | | | | | |_______|

####### ####### | ####### | -----___ ####### | \ ####### | \ #######| |#######| |#######| |#######|

software to enable that could be a problem.

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This email has not been checked by half-arsed antivirus software

Why are people pushing such an obviously poor solution? Picture this...

##### ##### ##### ##### ##### ##### ##### ##### ##### ===========

This is how the chip will look standing on its edge as the aspect ratio of width to thickness is 3:1. Do you think it is going to stay there between the pick and place and the reflow oven? Even when it does, do you think it is going to stay in this orientation once the solder melts? Just as chips tombstone, the surface tension can make them fall over too. Then it would be a real mess with the chip likely not centered well.

In fact, that is my real concern, centering. The 1206 is just over 10 mils wider than the pad. So if it shifts a bit it may short to one of the several nearby vias.

Maybe the right way to go is to use the inductor. I can't get this particular part a lower value than 1.5 uH. I'm not comfortable adding an inductor to the output of a linear though. Maybe I can find another part in a much lower value that fits the same pads.

I guess I'll wait to see what the assemblers tell me. They once put an

0805 part on 0603 pads in production. This likely isn't much worse than that.

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Rick C

Can they handle an 0204 MELF? That'll fit on a 1206 footprint nicely.

Cheers

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Syd

Not ignoring it, but this part is the same if not bigger than the 1206 resistor I am looking at. The other Harwin test points are the same size as 0805 and 0603 resistors which are too small.

However... I took another spin through the Digikey list of test points and found one by Keystone, the 5015 which is just the right size... Goldilocks! But this is hardly cheaper than the resistor jumper. Those are a fraction of a penny and this is a quarter even at qty 500. Not a big deal, but certainly not cheaper... maybe cheaper than the inductor, but not by lots! I wonder why a small piece of metal is a quarter??? Does it really cost so much more to make than an SMD resistor?

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Rick C

On Fri, 1 Jul 2016 04:45:19 -0400, rickman Gave us:

It is presicion cut and formed and plated metal.

I think I was thinking of and referring to a precision zero ohm resistor.

Even the wrong form factor will self center on the pads from the solder meniscus, unless the irregularity is extreme.

I just picked one. The one we use is different, and I never even glanced at the price.

I know ordinary resistors are cheaper.

resistor.

0 ohms +- 1% ?

;)

Cheers

Phil Hobbs

On Fri, 1 Jul 2016 04:07:31 -0700 (PDT), Phil Hobbs Gave us:

No... that is standard level. Cheap. At 0.1% they get a bit more pricey.

Resistors are made by the billions. Test points maybe in the millions per year.

A lot less perfected and optimized manufacturing method and more costly finished product, and likely a higher QA fail rate. Higher price result.

I'd think a 1206 on its edge in danger of getting its metal terminations ripped off.

Nah, I was too hasty. Even 0.47uH looks a little ugly--30 ohms at 10MHz.

A 1206 zero-ohm resistor leaving 14 mils clearance doesn't sound awful. They *do* self-center. But beware: their current-carrying capacity varies greatly, and some are surprisingly wimpy.

Cheers, James Arthur

Almost always [0..+oo%]. They cherry-pick the others for military use.

Cheers, James Arthur

No need for that sort of accuracy. I'm not using it for its resistance, it's just a jumper.... ;)

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Rick C