Future: 0603 versus 0402 parts

My production people hate 0402's... they tombstone a lot. We still use

0805's when there's plenty of room, 0603's for tight stuff, occasional 0402's for picosecond stuff where it matters.

You can still buy lots of 1206's and 2010's and such. They're not going away.

Looks like some parts are appearing only in those drecky leadless/chipscale packages. Yuk.

John

Un bel giorno Joerg digitò:

I have to say that it's easier than I thought. They are still relatively easy to hand solder; of course you need a microscope, but I wasn't able to solder 0603 without it either. The problem with 0402 is the production: a lot of assembliers still have problems with very close 0603 components, with 0402 it will be even worse.

I think that very soon BGA (and hidden pins in general) will be the default for all the ICs, not only the hundreds-pinned. You can already see this trend, there are already a lot of logic ICs - even with few pins - with BGA and/or flipchip package options. This worries me a lot more than discrete components; 0402 can still be handled, but BGA means that you have to change completely your procedures (design, PCB routing, prototyping, testing...).

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emboliaschizoide.splinder.com

Hmm, I never had tombstoning with those. OTOH nearly all my clients contract out circuit board stuffing so they don't have to bother with that. Sometimes even the whole production. Sometimes I have a chat with the contract producers and they'd tell me if they weren't happy with parts of a design. Like when zeners began to miss data sheet limits I had an instant email from China about it.

Good to know, thanks.

I really hate it when there is a cooling pad that must be soldered, on parts that consume less than 20mW. Arrgh. I have begun to shun parts that don't come in TSSOP. Too much trouble. And when they stop the migration path for a part at the SOIC level that is a red flag in terms of remaining product life.

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Regards, Joerg

http://www.analogconsultants.com

I use 3x glasses and do it sans microscope. Unless the client has a camera-monitor setup.

Hmm, haven't seen that trend yet. Most of my stuff (analog and logic) is migrating towards TSSOP.

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Regards, Joerg

http://www.analogconsultants.com

As a "board stuffer", I'll say a few things.

As you get smaller, assembly houses have to be better to do it. 0603 is a "knee" level for that right now. As the placement is needs to be more accurate for smaller parts, more will be off one pad and tombstone. However, with better equipment, the difference isn't as bad.

Bigger parts are more robust in many ways. Thermal transfer,mechanical strength, etc. Board contamination, water, etc., is less likely to cause an issue with larger parts.

I say use the biggest parts you can fit in the required space, all the way up to 1206 (the price is not that big a difference). There is no real good reason to go smaller if you do not need the space. If your cost of 0805 vs 0603 is killing your margins, you are better off examining new markets or products. Yours are dead.

Yes, I know about high-speed and using smaller caps. But whenever I here this, I see 0201's on a board running 20Mhz or less. No, you are not improving anything then.

Un bel giorno Joerg digitò:

And at the end of the day you can still find the way home? ;)

Same here, SOIC is becoming quite a rarity in my designs, almost everything is TSSOP. But more and more frequently, when you open the datasheet of some logic IC, you can find the microscopic BGA package options like VFBGA and WCSP, or perhaps when you are lucky the (still annoying to hand solder) QFN:

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emboliaschizoide.splinder.com

Nope. Client brings me to the hotel. Then I only have to find the way to a local pub :-)))

BGA is a pain. You can't see whether it's soldered right. Luckily all the chips I need come in TSSOP. I was extremely glad when they even ported the old CD4000 series to TSSOP.

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Regards, Joerg

http://www.analogconsultants.com

I saw some 0402 tombstoning on a fairly recent batch of boards from a China assembly facility (SnPb process). Zero problems with the 0805s (no 0603s on that design).

You may not like the price, though.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

It's always good to hear from the folks who actually have to produce what we design. You guys really know what works and what doesn't.

Well, looks like I should stay with 0603 then. 0805 would become a bit tight on this board but I shall see when the schematics are done.

Nope. I have designed on the cutting edge in terms of cost for a couple of decades now. Most others cannot understand how a human being can possibly enjoy doing that. But I do. Then there are the devices that just have to be small. Medical disposables, for example. On many of those a SOT-23 would look like a boulder. I remember not being able to use a TLV431 because it didn't come any smaller than SOT-23 at that time.

I promise I won't do that unless necessary :-)

BTW, do you mind sharing the name or web site of your company? My clients are always on the lookout for good SMT prototype assembly.

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Regards, Joerg

http://www.analogconsultants.com

Use the largest you have room for, even if it is a 1206. Smaller is not "better" unless you need the room (yes, I know, small caps at high speed, but whenever I hear that, its on a sub 12Mhz design). A better machine is needed to place 0402 vs 0603, and those can be "limits" for certian places, meaning even those sizes may be marginal on placement. If you see alot of green on your board, why not use larger components the human eye can see? Why make it harder, potentially less reliable and dificult to repair?

If a few tenths of a cent is going to break your profit margin, your market is too old and ready to die. Reevaluate your products and markets instead of shaving pennies.

Sorry for the semi "double" post. Google groups sucks, but my ISP has no newsserver :( Seemed to not go thru the first try, then shows up later. Go figure.

I use 2x and 3.5x mag visors, and after a while with the 3.5x on, I can't focus on regular things any more. It takes a few minutes to re-adjust. So, I try to use the *weakest* lens that works for the part sizes I'm working with.

My last design (still debugging it ;) is primarily 0603 and tssop, with sot-323 transistors. The occasional ssop (0.65mm pitch) seems big to me now. I had SOICs on my last board, but only because it was a RAM array and I wanted to run traces between the pins without horrendously expensive fab costs, and it was a 5v design which limited chip selection.

But, I've done boards by hand with tvssop (0.4mm pitch) and 01005 parts. It can be done, and it puts the larger (hah) parts in perspective.

One of the problems with a mixed design (where there are also some large devices on the PCB) seems to be the paste. Too much and you get tombstoning, too little and the big parts won't solder reliably. Like those pellet stoves where they haven't figured out how to automate intake air. Throttle too high and it'll go out on "1". Throttle too low and it'll smoke on "3" or higher.

Actually a 1ohm 1206 costs roughly the same as a 10K in 0402, around $0.007. A 2010 size can pop to several cents. Still, I don't see a reason for anything larger than 0603 unless it is in a current sense path or RF bridge.

[...]

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Regards, Joerg

http://www.analogconsultants.com

That was for larger quantities.

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Regards, Joerg

http://www.analogconsultants.com

Interesting. 0402 caps in my case would only be 0.01uF and smaller though, the rest would be mostly 0805. But as Brian said, it may be best to keep it as large as practical. 0603 for resistors and 0805 for most caps is certainly in the cards on this design, maybe even 0805 for everything.

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Regards, Joerg

http://www.analogconsultants.com

Well, if you're buying them one at a time, it's mostly overhead.

Suggest you get quotes in production quantities where appropriate.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Yeah, lots of people have that issue. I feel blessed. My ISP changed hands twice, PacificBell -> SBC -> AT&T, but they always kept a nice NG access. Even binaries are allowed which is really helpful for schematics and photos.

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Regards, Joerg

http://www.analogconsultants.com

I tend to use 0603 and only go 0402 if I have to. There are a few reasons for this. From an assembly standpoint, as another poster said 0402 is a knee in the manufactures abilities. Also 0402 uses a different feeder for most P&P machines than 1210-0603 so often CMs don't have as many feeders for

0402.

From an electrical standpoint for caps there has been some recent research showing that in the smaller geometries (0402 and smaller) the caps do not hold there rated capacitance as well when they have a DC bias on them (as in used for bypass caps). I am still learning about this but apparently the actual capacitance value can go way down under DC bias for smaller geometries and this is not as prevalent for 0603 and larger.

Hawker

On 3/13/2007 4:01 PM, The digits of Joerg's hands composed the following:

??Use 0301 parts so that nobody can see what it is (or even if something is there)?? Seriously, i would pick the 0603.