Prototype oven recommendations

Ah! Different work process than me. I would, instead, have stacked the reflowed boards and did the secondary processing a day, week, etc. later. So that I am only focused on one activity at a time (less chance of forgetting some little detail -- especially on boards that are "made once", not repeatedly).

[The last cheesecake I made I realized I had failed to mix the *sugar* (gack!) into the filling -- because I was trying to prepare dinner at the same time! :< Thankfully, caught it 10 seconds after placing it in the oven so I was able to remove the filling, mix in the sugar, reassemble and restart the process! 100's)

I'll build a few hundred, total, (though different designs) and scrap the oven afterwards. Nor will they all be built at the same time. E.g., build one/couple of each design, as required (to characterize them as well as debug the software, etc.). Then, once satisfied, buy the balance of the components and fab the remainder. If a design change necessitates scrapping some *bare* PCB's... ... much preferred to scrapping a bunch of fabbed boards that "won't work" along with all the components thereon!

Reply to
Don Y
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Yes cleaning stencil can be time consumiong.

I have not paid $100 for a stencil or even a stencil pair, I think the MOST I have paid was about $75 for a pair of stencils 250 micron stainless steel for both sides of a board 350 x 250mm.

Often PCB houses I deal with do free stencils with prototype qty boards so no brainer on getting stencil even if it is 400 micron not so good for below 0.5mm pitch.

My largest quantity I have used stencils or even small toaster oven kit from Beta layout is 12, normal quantity is 2 (never do 1 always have a spare). That oven does 290 x 290 mm approx boards. Not wonderful but does the job had to replace elements (about $20 including shipping). The kit cost about $300 at the time and has more than paid for itself.

Looked at T-962 series an would only consider the ones on Ebay that have been OEMed to have different controller in for better control and profiles. Small outfit in UK who retrofit them or sell kit to modify them.

....

Well I do the layout and doing prototype build run on small boards in small oven saves time and hassle of getting kits for a fab shop or paying their costs for proto assembly. That way I know the right parts are used. Especially as often I am dealing with samples of chips not available in less than tray quantities. Dont get me on the huge box to air freioght 6 samples from Taiwan the chip was QFN 6mm x 6mm, the freighting box was about 750mm x 300mm x 250mm.

In some cases I have done one off systems including spares then got repeat orders because production was ramped up, so having known stencils helped.

--
Paul Carpenter          | paul@pcserviceselectronics.co.uk 
    PC Services 
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Reply to
Paul

So I guess you would never use a dishwasher to clean the boards? That has to seem very amateurish too, no? Ask JL.

Can you define "pennies"?

How are you going to select an oven based on this criterion, "avoidable rework"? Do ovens come with an "avoidable rework" index?

Everything you buy will have risk. Spend too little (or more than enough, but on the wrong unit) and you have problems. Spend too much and you just spend too much with little improvement in utility.

--

Rick
Reply to
rickman

It's not just a cost issue. You get to see if the artwork, silkscreen, mask, etc. *really* give you a manufacturable board (especially if you also want hobbyists to be able to fab them -- at their own risk). You might not realize (in layout) that the placement of a silkscreen legend makes it ambiguous whether component X or Y fits into a particular location. Or, that there is some mechanical interference that you didn't foresee.

Yeah, a fab house *can* spot these things. And, hopefully, convey ALL of them to you. Or not. If it's a local shop, perhaps you can drop in on them when you're in that part of town, etc.

IME (building prototypes for clients), it was *so* much easier to just build the first unit myself and see, first-hand, what the potential problems were likely to be. Of course, a different set of eyes, hands and tools might turn up *other* problems (I've had problems with pick-and-place in the past... hard for me to verify on my own :< )

I will be building some number of "first samples" -- true prototypes to actually verify the functionality of the design, software, etc. Easier to prototype in foil -- especially with the devices that I am using and some of the packaging constraints.

If any of the designs/layouts prove to be faulty, I can scrap the remaining boards (of that particular design); turn the crank, again; and repeat with the newly revised design/layout.

Once everything are proven "acceptable" (no rework or just minor rework required... some of which may be easier to do on *bare* boards), I will proceed to make the rest of the prototype *run* for the prototype *system* (quantity one).

[Though this will tend to be a staggered effort as the entire system won't be done at a single point in time with *just* the "first samples". Instead, I may finish producing *all* of the "design #6" boards before I build the *second* "design #2" board. E.g., the highest quantity design will be fabbed in many stages as I won't need *all* of them until the very last moment.]

I.e., I *know* how many of each design/layout I will eventually be building -- *I* am the customer! If I find someone who wants to produce more (for themselves or for sale), then I could hand off to them any tools I have acquired/created in the process.

Or, not. (e.g., they might want to make changes to the design going forward)

Reply to
Don Y

No not yet. Many times what I am building is on a tight shipping schedule. If the oven broke I'd be back to the hot air gun and there is now way I would make the schedule. So I bought a spare.

I have some ESD stackable trays I use. My sequence is I paste maybe

8 or 10 boards and put them in the trays. I have a little "box" that keeps them about 65F to help with the paste life. I stuff one and into the oven. While it bakes I start stuffing another, etc. Or depending on the board I might stuff them all. The stack trays really help.

The trick is to balance your paste life with how long it takes to stuff and bake.

Trying to do something like an oven rack is tricky and would be almost impossible with a double sided board. You have to be able to control the heat on the "other" side. Surface tension only goes so far competing with gravity.

I understand what you want to do, like baking loaves of bread. Not that easy keeping the temps right. Take a look at your paste temp profile. You need to ramp to, say 220C and then make that bump to 240C in 15-30 seconds depending on your profile. Then ideally need to bring that back down in 15-30 seconds.

Maybe. But I dont think it's worth the trouble. My stencils are normally 5mil stainless. The way I understand it (and could be wrong) you also have to post process the cut to clean it up so the release is better. I just order them and the stencil guys tell me the best choice. I have no desire to become a stencil expert.

--
Chisolm 
Republic of Texas
Reply to
Joe Chisolm

OK. So, in your opinion, it isn't the sort of device that just falls apart when you peel the chinese cardboard (box) off of it!

So your boards tend to be small-ish?

I was planning on using the drawer from the oven to "accumulate" the stuffed boards. So, I need space for the oven and enough elbow room to stuff *one* board (at a time).

I am hoping to decouple the two -- by not caring how long the bake cycle takes as I'm "done" stuffing before it *started* (so I don't have to drop what I am working on to attend to the oven's call).

"Oven rack" meaning *toaster* oven rack? I.e., have you had problems doing double-sided in your kit? (do one side at a time -- heatsinking the inactive side?)

As I mentioned elsewhere, external air handler would be an ideal way of doing this! Change air temperature nearly *instantly*! Of course, more wasteful of power and you'd need a place to exhaust all that process air...

Ditto. I don't want to be a reflow expert, either! Rather, like every other skillset, learn just what I need to do what I want and avoid the annoying details that address "the last 2%".

(sigh) Perhaps I should start calling in some favors. After all, folks forget they owe you if you leave them "banked" too long! ;-) And, it would be really annoying to discover folks retiring out of positions where they can be of help!

I guess I will have to deal with the dreaded telephone this weekend...

Thanks for your comments!

--don

P.S. Any suggestions re: the T-962C I mentioned? "A bigger version of the A?" Or, does the design not scale well??

Reply to
Don Y

On Fri, 05 Sep 2014 23:05:12 -0500, Joe Chisolm Gave us:

Paste life includes all time until the reflow run itself.

I am sure lead free has longer open air time than the old stuff.

The old stuff made way better solder joint IMO though.

Reply to
DecadentLinuxUserNumeroUno

In article , snipped-for-privacy@is.not.me.com says... ....

Have a look at these folks and their description of differences

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In their view it is underpowered has the same heater and fans as T-962A trying to heat a larger volume.

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Paul Carpenter          | paul@pcserviceselectronics.co.uk 
    PC Services 
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Reply to
Paul

for something you're only building one of stainless seems a needless expense, polycarbonate or paper might be better priced and sufficiently durable.

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umop apisdn 


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Reply to
Jasen Betts

Perhaps but lead-free has a very tight temperature profile. The difference in temperature between the solder melting and the parts wilting is very small and short (time). The PPoE had a lot of trouble with their lead-free solder process in a four-stage oven. LEDs, aluminum capacitors, inductors, and QFNs were the biggest problems. Balancing the profile between the needs of all of these was like balancing a pencil on its point. They bought a used multi-stage oven (eight or eleven, can't remember) in 2010, when manufacturing equipment could be had for pennies on the dollar, and the problems went away.

Far harder to get the same quality, that's certain. Harder to inspect, too.

Reply to
krw

On Sat, 06 Sep 2014 09:42:10 -0400, snipped-for-privacy@attt.bizz Gave us:

I'll bet that it a pure PITA.

We never had to worry about that at the lower temp older process either... unless the belt stopped.

So, we can at least say that the new RoHS stuff has cause better, higher temp polymers, etc to get incorporated.

One plus on a very short list. They have massaged a lot of the bugs out though... still.

I am sure it is still that way. Just not the PITA it was in the initial years.

There is still a lot of liquidous gear out there, but demand is higher as the economy lifts (a tiny bit) so the prices are higher in that market currently.

You mean now, right?

I used to be able to scan an 18 inch square board back in the 0805 days and literally just *see* any bad joints or tombstoned resistors, etc. in my periphery.

Now, I can't even count my fingers without a pair of reading glasses. (exaggerating)

Reply to
DecadentLinuxUserNumeroUno

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.

[snip]

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.

--
Chisolm 
Republic of Texas
Reply to
Joe Chisolm

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.

Reply to
krw

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

*bigger* one! And, it was relatively easy for him to convince the powers that be of the needless duplication of efforts involved. So, their Engineering staff now schedules prototype runs AS IF regular manufacturing runs (just incredibly tiny quantities!).

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! :< )

[I'll have to wait until next week for him to get me the details of what he has to offer...]

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

*off* to a fab house is just not time-efficient at uncovering these.

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

Reply to
Don Y

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

*should* draw 4000W to have the same *heating* capacity as the A (assuming the A is not OVERdesigned).

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...

Reply to
Don Y

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

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Reply to
WangoTango

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

Reply to
Don Y

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