Prototype oven recommendations

On Fri, 05 Sep 2014 22:13:24 -0700, Don Y wrote: [snip]

Some PCI size. Others in the 7x7 range. It varies. I do have some backplane boards that are 14x2 (I think it is). But those are TH connectors and such that we do by hand. I think the stacking trays are about 9x10x3.

The clock starts ticking when you apply the paste to the first board of the batch and does not stop until the last board reflow is complete. It's not so much an issue of getting the board out of the oven as it is getting the next board in the oven. That damn clock keeps ticking. If you are squirting pads with a dispenser it not too bad to do a panel or 2, stuff and reflow, do some more, etc. With a stencil the prep and clean up time is high so you want to do as many boards as you can fit in the working window.

The T-962[A] will do double sided no problem because the IR lamps are on top. A toaster oven with elements on top/bottom would be much more of a challenge. I have 3 designs that are ds and never had an issue with them. But it's generally just C R and L on the one side, maybe a discrete semi or LED here and there. The other side has the bigger parts. I really push for components on 1 side only. I only want 1 pass through the oven.

It's not the air temp that's important, it's the board temp. Throw in some 2oz or bigger planes and the thermal mass starts to add up. These little ovens have their limits. I have some x8 EMI filters that are a pain. I could not get the profile right to push enough heat in them and not cook the rest of the board. A big conveyor oven would have had no problem. That board is real low volume now so we just put those on by hand. I dont think we have shipped one of those boards this year so it's not worth the time or effort to change the design. [snip]

I think they all use 4 elements. As Paul Carpenter said in the other post, the extra volume makes things worse. I would not go bigger than a "A" unless you can find something with more power. I just shoved a L-com catalog in the tray. It is 10.5x8 and would probably be OK size for a board/panel. Bigger you will have problems, thick planes you will have problems. I have done 8 layer 1oz boards without problems.

The 962A works for me but if I could justify a larger conveyor oven I would get it. A PNP with vision would be more of a help.

FWIW, the time-temperature 'safe' band between adequate soldering and damage to *some* components has a fairly small area.

consider this one:=

And that's a semiconductor- some parts are more sensitive.

--sp

Best regards, Spehro Pefhany

That threshold varies widely among components. Some are fine "all day" at 200C but will wilt in seconds at 250C. To get a good solder connection the joint needs to get to 260C (most RoHS solder).

On a snuny day (aSt, 06 Sep 2104 13:07:40 -4000) it hepnepad snipped-for-privacy@attt.bziz wtroe in :

It was, in a small company, where I had to worry about the mess left, yes. Not so much anymore. ;-)

Right. The PPoE's process was golden with leaded solder but went right out the window, for a year, with the socialist solder. Along the way, we were surprised by the parts that caused the biggest grief. I would have thought BGAs would be a problem but not a big hunk of metal like a transformer. Wrong.

There is some of that but unless you're doing RoHS, most of it is wasted effort.

A lot has been learned, sure, and as you note, parts are better. I think it's pretty mundane, now. Everyone knows how to deal with it. The long-term problems seem to have been overblown. That isn't to say that the whole effort wasn't an absolute waste of time and resources, though.

I should amend the above to say that the *final* problems went away. A lot of them had already been solved by that time.

No, I think the lessons learned and the better tools and processes have leveled the playing field, at least for those with the resources to buy the proper tools. That leaves most of the "garage" outfits out, though.

You're just getting old. ;-) OTOH, at one time I thought 0805s were small. Now I almost trip over them (SC70s, 0402s, and .5mm pitch QFP/QFNs are the norm). A Mantis or OptiVisor helps.

Yes. That just means you need to be able to drive the temperature to *any* setpoint (up *or* down) "quickly". Hence my face/bypass musing!

There are specific specs in this document for the rate of heating and

than 30 seconds. The actual heating and cooling rates are given as maximums, but no minimums. The heating side does have a max total time of 8 minutes, but nothing on the cooling side. There is also a max time

I don't think this will be hard to meet as long as the oven has enough heating capacity. Certainly the cooling side will be easy to do.

You could use your house wiring to reflow...just plug that monster in!

Yes. I am hoping that *focusing* on stuffing *all* the boards (instead of stuffing, loading oven, stuffing more, unloading oven, reloading oven, stuffing more, etc.) and then baking *all* of them in one batch is a more efficient use of time.

I.e., if I had an "assistant" and staging area so one person could CONTINUOUSLY stuff boards while the other continuously services the oven, then there would be no "interruption".

Again, my cookie example: I can cut 20 dozen cookies from the (frozen) dough and lay them on 6 or 7 cookie sheets then baking ALL at once in a lot less time than doing one sheet, feeding it into oven, prepping a second sheet, removing first from oven, inserting second sheet, transfering removed cookies onto cooling rack, then starting to prep the *third* sheet for the oven...

There is a non-negligible "task switching overhead".

I think ours allows you to select which elements are on (bake vs. toast, etc.)

Understood. But, there's just not enough real estate on one side. The 1.25 x 2.5" (by about 1") envelope is pretty much fixed. So, I either find more "sides", smaller components, higher integration, etc. Keeping in mind that I want others to be able to make these as well eliminates a lot of options!

Yes. But, instead of radiant heating, if you expose the boards to preheated/"precooled" air (e.g., an external air handler delivers a specific volume of air at a controlled temperature) to the boards, they will track the temperature of that air.

I don't know how efficiently radiant heat transfers energy into materials (vs. passing them through a heated "fluid"). But, for sure, the elements aren't actively *cooling* the materials! Instead, the oven relies on evacuating the heated internal air mass.

If, instead, the temperature of the air being pushed into the enclosure was actively driven to a lower temperature (even ambient), then you've moved the control loop outside of the oven's interior.

As the oven would *continuously* be exhausting air (even during its preheat cycle), you can monitor the exhaust air temperature to get a feel for how much energy is being absorbed (by the oven's interior and the items placed therein). (there may be other things worth monitoring as well?) You also know the maximum temperature that the surfaces are exposed to -- that of the incoming air.

The amount of heat you can pump in is then a matter of how much air you can move, without jostling the components.

Dunno. I don't design reflow ovens.

Well, first call was met with, "Sorry, we decided it was easiest to farm out all of our fab -- even the engineering prototypes and first manufacturing samples". I am waiting for some number$ to get a better idea for how much this decision is worth to them...

However, second call was more productive! I've been offered a small oven that another friend had previously used in their engineering department. Apparently, their Manufacturing guy felt threatened (?) by Engineering having a reflow oven -- when *his* department had a

While this seems like a good deal (for me), it means I have to either let him ship it to me *or* go for a visit (I detest travel!). SWMBO has already given me the Evil Eye as she knows if I go for a visit, I'll end up driving a *truck*/van back! And it won't *just* have a reflow oven in it! (she was thrilled when I stopped my annual pilgrimages to visit him as it slowed the "rate of accumulation" here! :< )

Still waiting for third call to be returned. Perhaps "third time's the charm"?

So, they are *longer* elements (2500W vs. 1500W)? I will have to see if I can find any more detail. OTOH, the increase in size suggests a proportional power level would be in the 4KW range.

I have not yet read the review he mentioned. Still rolling out of bed...

I can stick to 4 and 6 layer boards. As the boards are small, no real need for extra thickness. May have some problem with copper thickness, though, as many of the devices I am using rely on a heavy copper plane to pull heat away from the device. Thermal reliefs kind of being contraindicated in those cases! :>

Worst (as far as size) for me are the boards for the network switch. They tend to be larger (in at least one LONG dimension). Maybe I can revisit that design and partially cannabilize an existing switch (though it would REALLY be a kludge!)

OTOH, there is nothing *forcing* me to adopt the typical form factor for such a device. I *could* rearrange things to better exploit the capabilities of a smaller oven... might *look* weird, though...

I don't want to be in the board fab business. If there was a fab shop "next door", I would gladly give them the business: walk over in the morning to see what problems they have encountered; wander back home for lunch; drop by any time they stumble on an "issue" that I need to examine/address; etc. Let *them* acquire and maintain the equipment, train/supervise the staff, etc.

It's like having a tech build your prototype so you know what sorts of issues he -- and, ultimately, Manufacturing -- will face. Sending

(Here, any such industry would be at least half an hour drive each way... perhaps considerably more! I live in a high-tech wasteland...)

Obviously not the *same* heater -- as the C version draws 2500W while the A draws 1500. But, the increased size suggests the C

Likewise, a *third* fan would seem to be required to similarly scale the capabilities of the A.

Without photos of the interior (I will start searching once I am awake), its hard to know for sure but I suspect they just put *longer* heating elements in place instead of *more* elements (the latter giving better coverage).

It really *does* seem like the better solution is an external air handler approach. Size *it* for the volume that you want to control. And, the maximum temperature that you want to be able to attain. The *rate* of temperature change would be easily accommodated by the face/bypass damper: 25C to 300C (air temperature) in 0.5 seconds!

As a compromise, Hamilton's "convection oven" approach may merit further exploration. Especially if you rearranged the elements to locate all of them *above* the work (and had good temperature sensor placement).

(sigh) I had planned on doing OTHER things today...

I bought one of these low cost things, and it has served us well :

Yes, Joe (& Wouter) comments agree.

I've been offered a larger oven (more in line with my initial goal). But, another friend has offered to fab the boards for me -- *if* doing so will be "uneventful" (i.e., no problems encountered in their manufacture).

So, I will rethink "dry fitting" each of the designs to verify the boards are manufacturable. Then, just kit everything up (probably in two separate batches so I don't have to invest in *all* of the silicon before needing it) and let him assemble them for me. (I'll do all the testing since it is largely automated).

If I have concerns about a particular design, I may opt to build *a* prototype, myself. In which case, a *smaller* oven (than my original goal) may be a worthwhile thing to have available, here -- even if it only gets used one or twice!

Thanks, all!

--don