soldering components on larger sized pads

Only if you are willing to accept that it will not meet even the most basic commercial spec.

The inboard edge of the pad must contact the inboard edge of the termination on whatever part you wish to place there. You cannot count on a "web of solder" to bridge any gap that might be there with a part mis-match.

The extra solder isn't an issue, but "acceptable contact criteria" could be. It depends on the application. For proto... sure, no problem.

Depends. You can do it, but I'll venture to guess that you will end up with a higher than normal incidence of tombstoned parts in automated assembly. If this is a deliverable, I wouldn't do it as you may run into thermal failures where the end cap termination is over stressed. The pad dimensions have been carefully chosen to minimize stress failures of the termination.

BTW, 0603 parts are easy to hand solder. 0402 is where things get a bit harder.

-- Mark

The short answer: For production, no. Any reputable assembly house would reject that job.

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Bulloney. We have resistor/cap/resistor stacks added to our PWAs at the 0603 level. If we wanted an added, hand placed part on one of our assemblies, our contract assembly houses would not have any problem with that. Bridging a gap they would not do, but if the part fits onto the pad for the next size up, and can be soldered, they'll do it.

As long as it can be manufactured to the IEC standard in the class level requested by the customer, any reputable contract manufacturer in my country would take the job, and quote it appropriately.

When and if we re-spin the board, we'll incorporate any changes we may want to add. The stacks may well be exactly what the designer wanted, and is can and is manufactured to industry specs every day.

Jamie was referring to automated assembly, meaning machine placement. I can't imagine they'd agree to auto-place 0603 parts on 1206 pads. The only way they'd probably do it is with a "no-guarantee that it works" clause. Something I would not agree to as a manager, on neither side of the table.

By hand, yes, you can do all sorts of things. I am just having a tech rework boards where we need 0805 where a large inductor was, because of a major spec change. Not big deal. But automatic placement? No way.

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I am fully aware of what he was talking about. I ALSO CLEARLY stated that it would be a hand placed item in most cases.

That all depends on the pad outline chosen.

You obviously do not understand how contract manufacturing works. They provide the customer with the end product THE CUSTOMER wants. You do understand what the word "customer" means, right?

You obviously have little grasp of how the industry works. You seem to have that "manager mentality" of about four decades ago. That shit don't get it these days. What you need is that "Phelps can do attitude".

You ain't real bright if you think that the vast majority of PWA assemblies are machine place only. Nearly every PCB assembly requires hand operations be performed on them, especially in conduction cooled environments where bonding operations are performed.

Automatic placement can be done if the part in question is epoxy staked first. Then, the part is in place, and all assemblies can be hand soldered and still look the same. Then the assembly goes through the normal pick and place operations.

Sure hand operations increase the per assembly price quote, but if one wants to play, one has to pay. There are plenty of instances where a PCB re-spin cannot be performed and the assembly has to have any changes made to the circuit added, by hand, after the main assembly process.

Quote from OP: "... but for automated assembly is it ok to put smaller (and cheaper) 0603 sized components on these 1206 pads reliably?"

He asked whether it can be done automated. It can't be, or at least shouldn't be.

In my field performance of a product is critical, sometimes the life of people depends on it. We do not kludge stuff. Neither do our contract assemblers because their liability is on the line.

Have you ever worked in medical devices, aeronautical, automotive?

Sure, we also have the occasional hand placement. But other than for prototypes they won't put a 0603 part on a 1206 pad. At least not in med devices and stuff. I would never, ever sign an ECO to that effect, nor would I recommend my clients to do that. Something goes wrong, an expert witness finds the kludge and plaintiff's counsel will tear you apart in a jiffy.

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Didn't we determine he was an HVAC control circuitry technician or something like that? :-)

In your line of work, Joerg, are vias in pads considered reliable (for automated assembly)?

Joerg wrote in news:EHCqk.18675$ snipped-for-privacy@nlpi067.nbdc.sbc.com:

[snip]

[snip]

I have 2 basic "dummy" questions:

- If solder is used to fill in a connection that otherwise doesn't reach, wouldn't the difference between the conductivity of the copper (of the component's wires/connectors and the boards tracings) create a lot of problems?

- If a component can't reach the place on the board it's supposed to connect to, would it be workable to solder a small additional bit of wire that's teh same material and diameter as teh component's connector?

Thanks in Advance!

- Kris

I wouldn't put a 0402 device on a 1206 pad for our deliverables either. Lives aren't at stake, but the company reputation sure is, especially since ship time can cost $30k per day and you have a limited window of opportunity due to ship scheduling.

-- Mark

Not unless the component in question is something like a milliohm-range current sense resistor where the tiny difference actually matters.

Or perhaps if you go above a handful of GHz in frequency... you can definitely tell the difference between "nicely" soldered RF connectors and those with lots of excess solder on them at, e.g., 6GHz on a network analyzer. (Not that it usually matters, though.)

Yes, and you can use pretty much any wire... something like 24 AWG wire is all of ~25 milliohms per foot, and even 30 AWG wirewrap wire is ~100 milliohms/ft. (Varies somewhat depending on exactly how the copper is drawn, though -- only important if you're planning to build homemade current shunts or fuses.)

---Joel

No idea ...

Very frowned upon by the assemblers. I tell my layouter not to do that. I also tell him every time not to use the default trace width which is usually 8mils or 10mils. No reason for that and it costs reliability. Other than that he knows a whole lot more about PCB fab than I ever will and I leave the rest to him.

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As Joel said, ok for "normal" resistor values but not for current sense shunts and stuff like that. However, I wouldn't ship things like that because chances are that mechanical stresses will eventually fracture the solder bridge and then you've got a grumpy customer. Then another, and another ...

For a prototype, why not?

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"Joel Koltner" wrote in news:aBDqk.21633$ snipped-for-privacy@en-nntp-02.dc.easynews.com:

OK, these things are less critical than I'd thought - thanks, I appreciate the informative answer :)

- Kris

If you have the space for it, I'd agree there's no reason for it. As for costing reliability though... is this really true anymore? With the "standard spec" trace size usually being 6mils these days, I wouldn't imagine there's much measurable difference between the reliability of 10mil traces vs. e.g.,

25mils?

I asked the "via in pad" question because I've seen it being suggested more and more as a means of reducing parasitics a bit and packing a bit more onto a given PCB, which suggests that assemblers might be getting better at. I've used them myself (with an assembly house that said they were fine), but it was just run-of-the-mill commercial products, not medical gear.

---Joel

Well, I have seen more grief in this area than I cared to see. The thinner a trace the easier it breaks, especially with this dreaded habit of not rounding corners and not doing trea-drop pad entried. That's usually where stress breaks happen. Ok, most of the stuff I design gets quite a beating in the field.

Thing is, when there is enough space why default to the skinniest trace? Just to make the autorouter happy?

The worst stuff I've seen is when designers didn't realize that there was more current flowing than the trace could handle. One of the units I got for an investigation was still emitting such a stench that I had to close the lab door and open a window.

Technically it can be ok but is messes with the thermal properties of the pad and it ain't all flat anymore. The only time I ever did that was where I had to, on a nickel plated land for a huge lug. This was screwed on and we needed a connection that could sustain a constant 100 amps.

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I knew a digital designer who was on a tight schedule to get a fancy new

16-bit microcontroller board done (this was ~15 years ago), so he whipped out the schematic and asked the PCB layout guy to get it turned into a board ASAP. PCB guy did so, board came back and... didn't work.

Digital designer man quickly ascertained that the problem was Vcc which, instead of being the 5V that it was supposed to be, was something closer to

4V. It seems that PCB layout guy -- in the name of saving time -- just told his auto-router to do the entire board using the default net (8mils, I'd guess), and the new CPU was rather power hungry (a handful of amps) and pulled enough current far enough along a solitary 8mil trace to suffer a volt of IR drop.

Digital designer man ended up having some techs manually solder on some fat wires in parallel with the power supply traces. :-)

In this case the PCB layout guy arguably wasn't very good, although I'd still lay blame with the designer for not properly reviewing the layout before he gave the go-ahead to have the board fabbed.

---Joel

Joerg wrote in news:HQDqk.34912$ snipped-for-privacy@nlpi066.nbdc.sbc.com:

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I'm sure it's always best to have good solid connections ;) , but it is interesting that such a thing is more tolerant than I'd expected. Good to know (in the "small errors aren't necessarily catastrophic" department ;) ).

I'd guess, though, that for a production item, or an item to be provided to an end-user, that sort of patch would bee too prone to breakage.

Interesting, tho' - thanks for the info ;)

- Kris

It depends... shipping boards with "just a few" blue wires (tacked down properly) or small board modifications (e.g., tombstoning a couple of 0603 parts when there's only one pad) is not that uncommon a commercial practice -- it's often still "reliable enough." Joerg is in the medical field, though, where reliability is a much bigger deal since it get pretty directly translated into liability.

If Joerg were running Microsoft, we'd probably still be running DOS, but at least it wouldn't have any bugs. :-)