Re: Future: 0603 versus 0402 parts

On Mar 13, 7:52 pm, Joerg <notthisjoerg...@xxxxxxxxxxxxxxxxxxxxx>
wrote:
Spehro Pefhany wrote:
On Tue, 13 Mar 2007 22:51:16 GMT, the renowned Joerg
<notthisjoerg...@xxxxxxxxxxxxxxxxxxxxx> wrote:

John Larkin wrote:

On Tue, 13 Mar 2007 21:01:41 GMT, Joerg
<notthisjoerg...@xxxxxxxxxxxxxxxxxxxxx> wrote:

Ok, have to decide whether to default to 0603 or 0402 for resistors and
stuff on a new design. Wow, this time I am not size constrained.

Looking at Digikey it comes up with 143 pages (has risen) for 0402
resistors and 218 pages for 0603. Looking at prices 0603 still has a leg
up, around $0.003 for a 10K while its 0402 counterpart runs about twice
that. Is 0603 going to be a good choice for the next years? Or better
stick to 0402?

Of course from a debug point of view I hate to deal with 0402. With
chips the situation seems to be more clear cut. Things definitely seem
to be going TSSOP there.

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.

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 *** limits I
had an instant email from China about it.

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).

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.



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

Good to know, thanks.

You may not like the price, though.

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.

[...]

--
Regards, Joerg

http://www.analogconsultants.com- Hide quoted text -

- Show quoted text -

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.

.

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