1. Home
  2. Electronics Design
  3. BOM minimization

BOM minimization

Our latest game is BOM minimization, namely using the least number of different parts on a board. The guideline is that each BOM line costs a dollar or two for every board we build... purchasing, kitting, p+p setup, all that.

The one I'm doing now has 100r, 1K, and 10K resistor quad-packs, so they are used in various combinations, like 50r terminations, voltage dividers, whatever. If we need 100r somewhere, we'll use a quad even if we waste three sections.

I need 1.2, 2.5, and 3.3 volts, from a 5v rail.

formatting link

(I admit that I spiced it and fooled around with connections, rather than doing the arithmetic by hand)

The risk with r-packs is that things are hard to change, so you have to be extra sure everything is right.

We're setting up our new full-auto p+p machine, and we want to have some number of feeders, 20 or 30, that never change. These three r-packs are candidates.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation
Reply to
John Larkin
Loading thread data ...

Kitting is one of the weirdnesses I never understood after moving to the US. It wastes resources to no end. So at the company I worked at that was one of the first things I ditched and we went Kanban. Hired an aerospace production manager who was fully on board with that and was used to it. One of the best hiring decisions I ever made.

It's a very good thing to reduce parts variety in a BOM. Another thing that makes sense (although some folks will never understand that) is to also max the tolerances. On one of my designs that's now running for about 20 years in production the Chinese contract assembler wanted to know which resistors could slacked off to 5%, 10%, or even 20%. It required 1/4h of billed consulting time to do that and the client had that back in a jiffy. For example, there is absolutely no reason why a pull-up resistor has to be the default 1% metal film.

That looks like a post-Zeitgeist shot, a bit blurry :-)

I admit that I also do that a lot. Maybe that's why the batteries in my HP-11C last >15 years.

They also eat a lot of real estate if you use too many of them.

I'd add 100k and 1M, for pull-ups and voltage detection in eco-friendly or battery operated gear if you design any of that.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

If you want to stuff a batch of boards, parts have to be pulled from stock and loaded into feeders for placement. Sometimes we send boards and parts out to an assembler. That is "kitting". Kanban has its own hazards, like lead time problems holding up building a batch of assemblies. We build small batches, 3 to 100 boards typically.

We just buy tons of the cheap parts and keep them in stock. We avoid counting parts by just pulling off reels, and returning the partial reels to stock after a build batch. The BOM minimization game makes that work better.

We only buy 1% standard resistors; they don't cost enough over 5% to be worth stocking. We do have exotica, like 0.05% thinfilms, here and there.

9AM. Handheld. Clicked "sharpen" three times.

The quad pack that we use is 1206 size, net, smaller than even two

0603's and their ref designators. Using the packs seems to save space.
10K is a pretty good pullup. We're not power sensitive. 
--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

We did away with that as well, by sending the whole enchilada to the contract assembler. No matter which boards were on order there. That saved a lot of labor and floor space.

The computer has to function impeccably well for Kanban and people must have good self-discipline and training. Stock goes low on something -> press a button. It does require slightly higher inventory levels. That was a hard sell to our CFO but I justified that by the (huge) savings in labor and floor space that we used to have with kitting. It was crazy. They use to have people sits there and literally ladle out the gazillion parts required to build xx number of systems at a time.

Since leadtimes are in the MRP system and build forecasts are as well, we managed inventory quite well and in systems assembly there were no line stops in all those years.

I remember that a Texan was sent in to audit this, probably since it was so unusual for the company. After the tour he said something like "Dang!" (pronounced daiaing) "Y'all make sure the computer is never gonna be off, ya hear?"

That's almost Kanban style.

You guys don't make consumer products, that's a big difference.

[...]

Ok, I am used to 0402 and no ref des'es.

Well, this time Cal-ISO said there's going to be enough electricity. I am not holding my breath though. Much of my stuff is battery or solar powered. Especially the battery-only gear is super-critical, where clients give me specs such as watt-seconds per circuit action (not watt-hours).

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

For stuff like $600 FPGAs, we still count out individual parts!

We are running below 15% parts cost, so we don't worry too much about cost. We're basically selling IP, expressed as the way the parts are connected. Picasso didn't price his work based on the cost of paint.

--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

... Kanban has its own

Seriously, we did not.

Because he didn't cater to the motel room wall decoration market.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Matadors. Cats with big eyes. Not his thing.

--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

Not a velvet Elvis in the bunch, either.

Reply to
krw

At what point do colored golf balls, "water spiders" and all that other automotive company jazz just not make sense?

Say you're building 50 boards. Why not just have the parts all ready to go instead of waiting until you run down to 2 PCBs before ordering more from another country to save 2 feet on some shelf somewhere in the back room? I'm sure somebody got too excited about JIT and ended up wasting lots of time and money. I've always wondered how big and busy you need to be to justify it.

In the automotive business, I see it makese sense as they're churning out huge numbers of products almost nonstop, and running out of driver side seats would be a show stopper to a production line, while at the same time storing 30,000 driver side seats would be stupid as well.

Reply to
Cydrome Leader

That depends on what you are building. I've worked in two scenrios where Kanban clearly made sense.

a. Mass production, to the tune of 50,000 to 100,000 units per year. Kitting that would be absolute nonsense and luckily was never done.

b. A few dozen machines/month. But very pricey, like luxury cars. Kitting was done and it wasted lots of time and resources. So we discontinued it and went Kanban. Actually the whole idea came from the automotive industry and from a time when production volumes weren't very high. From Toyota, actually.

You need a well oiled materials management system for Kanban. The system must always know (about) how many driver side seats are left and how long it takes to get new ones.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Kanban also requires that the buyer have overwhelming economic clout over suppliers, so that they don't dare miss a delivery. Small companies don't have that clout.

Luckily, most electronic parts, unlike car seats, are small and cheap and come on reels, so we can just keep a lot of parts in stock.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation
Reply to
John Larkin

That is one of the reasons why we went with a contract assembler. Many of those are large and thus have the required clout.

Jelly bean parts, yes. But if it's $xxx ICs the CFO will be unhappy if there is too much inventory revolving around.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Sure, 0402 resistors are $5-$10/10K reel but $600 FPGAs are a bit expensive to stock, just in case. The shelf life isn't all that long, either. Then there are the jurisdictions that tax inventory.

Reply to
krw

That's a really crap way to configure your regulators, especially from a 5V rail. Do you even read the spec sheets on your parts?

Reply to
bloggs.fredbloggs.fred

Depends on the current levels. Stacking voltage regulators theoretically makes the upper ones quieter--the 2.5V supply would be 3 dB quieter than the 1.25V one, relatively speaking. Using a resistor pack is one reasonable way to do that, especially if (as in JL's case) the pick-and-place costs are comparatively high.

What didn't you like about it?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

What's wrong with it? I sort of like that arrangement. The 100 ohm quad-pack was already on the BOM.

You are always such a downer. It's not good for you.

formatting link 

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation
Reply to
John Larkin

FPGAs and uPs don't care about quiet!

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation
Reply to
John Larkin

Neither does yo' momma. ;0

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

.JPG

the ones that have PLLs and ADCs might care about quiet on some supplies ;)

-Lasse

Reply to
Lasse Langwadt Christensen

JPG

1) He already has ripple rejection 60dB below radiated pickup if he's runni ng off a regulated feed to the regs, 2) he needs to pay attention to that w orst case 5mA quiescent (not adjust pin) of the 1117's, 3) any kind of high frequency disturbance on any of his loading is coupled to all the other re gulators more or less.
Reply to
bloggs.fredbloggs.fred

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.