Re-Flow.. Kitchen Aide (Convection Bake...Model # KCO223CU)

hmlittle59 · 2017-07-18 04:34

Hello All,(Home MADE re-flow oven EXPERTS)

Just realized that we have this unit that we NEVER use and want to make it my Re-Flow oven. Will this work and what else will I need (Paste/Stencil)?

My PCB has 346 pins....(292) are SMT (48 pin Parallax interpreter) and its becoming a real struggle to solder. Just added 32 more pins...ouch.

1) 450 f/ Broil
2) sliding rack

Thanks for ANY help and insight
added a link.
[url="https://kitchenaid.com/shop/-[KCO223CU]-400530/KCO223CU/"[/url]

Phil Pilgrim (PhiPi) · 2017-07-18 05:40

I like the idea of a convection oven, especially for larger boards. I have an infrared toaster oven without the convection feature. It's fine for small boards, but larger boards heat unevenly.

My recommendation for solder paste is a product called "Zephpaste" (63/37), available from Zephertronics. I've had a syringe of this stuff for years. I keep it in the fridge, and it hasn't gone bad yet. By contrast, a similar Kester product turned to cement in the syringe in less then a year.

A paste stencil is always a nice thing to have. But for one- or two-off small boards, applying dabs of solder paste directly with the syringe works fine. Just keep some solder wick on hand to soak up solder bridges when they happen (and they will).

Good luck with your project(s)!

-Phil

WBA Consulting · 2017-07-18 08:01

Should be a worthy piece of reflow equipment. Here are some notes on my reflow processes with my toaster oven (still using it the same way):

Step by step details for building my PowerTwigs with toaster oven:
http://forums.parallax.com/discussion/comment/983326#Comment_983326
and
http://forums.parallax.com/discussion/comment/1306664/#Comment_1306664

Comments about characterizing your oven to determine temperature ramp rates for optimizing your profile if needed.
http://forums.parallax.com/discussion/comment/1187950/#Comment_1187950

I use a 5 mil thick polyimide film (kapton) stencil for my PowerTwigs (cut on an Epilog 75 watt laser) and for my M44D40+ Propeller QFN Module, I have a 4mil stainless steel stencil.

T Chap · 2017-07-18 14:43

You need to consider the heating profile. You don't want to just turn it on 450 and and leave it. It may be that the temperature as it heats up has a slow ramp but take note of the different stages of an ideal heat profile to avoid damage to your parts. This means you may need to set a timer for a 1.5-2min preheat stage etc.

hmlittle59 · 2017-07-18 16:30

Hello,

Thanks for the feedback.
Phil, my PCB is a 4 x 3 single sided, would this oven be OK?
Been looking a YouTube videos and reading WBA's write ups. Thanks for the Link.

T Chap, not clear on what you mean by preheat stage. Do I wait before I put the board in or do I remove as soon as the solder flows from a cold oven?

Use to watch it at my old job years ago, but that was on a conveyor machine.

Thanks again

Phil Pilgrim (PhiPi) · 2017-07-18 16:56

A convection oven should be able to handle a 4" x 3" board.

I put my boards in with the oven cold. Then I set the oven to the preheat temp for about 90 seconds, then to the soldering temperature. From there, I keep an eye on the board, then turn off the oven and open the door once full reflow has occurred. (If your yellow tantalum caps turn brown, you've left the board in too long.

)

Here's a typical temperature profile for 63:37 solder:

For this reason, it is important that the oven have an accurate thermostat and a heating element that can change the temperature quickly. Mine has IR elements that do the job pretty well.

-Phil

hmlittle59 · 2017-07-18 20:17

Thanks Phil,

I think that I understand now...will see after the first run. Been checking on Stencil cost and turn around time.
And to pile it on, my Data is not coming through to the Parallel LCD. The debug screen is showing some Data I put in for test purposes. BUMMER.

Thanks again
Will need more help after material gets in.

Phil Pilgrim (PhiPi) · 2017-07-18 21:11

BTW, two of the reasons for the preheat and soak times are that they allow the volatiles in the solder paste to evaporate and the flux to "activate" (whatever that means) before the tiny solder beads begin to melt. You can read more about it here:

https://en.wikipedia.org/wiki/Reflow_soldering

-Phil

Cluso99 · 2017-07-19 01:27

I use OSH STENCILS. They are cheap and work well!

I use them on all my smt boards now including my P8XBlade2 which has 0603 parts.

https://oshstencils.com/#

hatallica · 2017-07-19 12:29

Phil Pilgrim (PhiPi) wrote: »

A convection oven should be able to handle a 4" x 3" board.

I put my boards in with the oven cold. Then I set the oven to the preheat temp for about 90 seconds, then to the soldering temperature. From there, I keep an eye on the board, then turn off the oven and open the door once full reflow has occurred. (If your yellow tantalum caps turn brown, you've left the board in too long. )

That basically describes the process that I used with very good success, even with a really cheap toaster oven. Running a scrap piece of PCB will help to boost your confidence prior to baking your boards.

Now, I use a convection oven that is more like the one that was linked (Black & Decker TO1675 ... very inexpensive). For grins, I rigged it up with rudimentary PID temperature control with a Propeller. While the controller requires less babysitting, the results were equally satisfactory with the manual process of preheating and watching for re-flow.

If you use a stencil, then don't forget that you will need to also have some type of squeegee. The stencil maker may offer an inexpensive tool. In a pinch, I have used an old credit card or putty knife.

A side note on Preheat and Soak, is that it also helps to reduce hot and cold spots on the PCB. Large components and large copper planes will require a bit more time to warm up. Thermal shock is not likely a concern, as neither of the ovens that I have used would ramp faster than 1-2 degrees C/sec.

And one final note ... be careful once you see reflow, turn off the oven, and open the door. Components are floating on melted solder that still needs to cool by about 30 degrees C before it solidifies. An errant bump could cause a frustrating mess.

Cluso99 · 2017-07-19 15:09

Old credit card works perfectly

hmlittle59 · 2017-07-19 22:36

Hello Again,

Phil, what is soak time and is that happening before the pre-heat or part of the pre-heat? Thanks

Cluso99: Wow, those prices are over a $20 + swing from Pololu.com...WOW!!! Thanks

Thanks again

WBA Consulting · 2017-07-20 00:15

Soak time is the "flat" part of the preheating cycle where the board temperature is allowed stabilize (or become uniform across the board) This is also where the solvents from the flux evaporate and the cleaning function of the flux occurs.

In "professional" manufacturing (aka my day job), apart from paste and oven manufacturer recommendations, we utilize a few industry standards to write our own procedures for how we control our reflow profiles and oven recipes. The two main standards are IPC-7530 or IPC-7801.

More helpful public docs:
We use KIC profiling equipment, here is a basic Best Practices document
http://kicthermal.com/wp-content/uploads/2012/11/Best-Practices-Reflow-Profiling-98675.pdf.pdf
We used to have Conceptronic ovens, here is a good how-to series of PDFs
http://www.conceptronic.com/products/solder-reflow-technology-handbook/
Section 1 has a good explanation of flux in the reflow process (starts on page 4 of section 1 PDF)
Section 3 explains reflow steps in detail

MikeDYur · 2017-07-20 21:19

Thanks to you guys, this is something I want to try.

Say a 2 x 3" board in the kitchen convection oven once a month, would that pose a health hazard?

Otherwise it is something to look for at a garage sale.

EDIT: Maybe a good oven cleaning by high temperature after the process.

Phil Pilgrim (PhiPi) · 2017-07-20 21:28

MikeDYur wrote:

Say a 2 x 3" board in the kitchen convection oven once a month, would that pose a health hazard?

Once you've used an oven for soldering, it's unsuitable for use with food -- ever again. Just put it out of your mind.

-Phil

Publison · 2017-07-20 21:35

Phil Pilgrim (PhiPi) wrote: »

MikeDYur wrote:

Say a 2 x 3" board in the kitchen convection oven once a month, would that pose a health hazard?

Once you've used an oven for soldering, it's unsuitable for use with food -- ever again. Just put it out of your mind.

-Phil

+11 NEVER AGAIN.

MikeDYur · 2017-07-20 21:37

Phil Pilgrim (PhiPi) wrote: »

MikeDYur wrote:

Say a 2 x 3" board in the kitchen convection oven once a month, would that pose a health hazard?

Once you've used an oven for soldering, it's unsuitable for use with food -- ever again. Just put it out of your mind.

-Phil

Ok got it, there is no half-life.

Wonder how many people have heated their lunch in one or on one, so as not to be inconvenienced.

hatallica · 2017-07-21 11:16

MikeDYur wrote: »

Ok got it, there is no half-life.

Actually, half-life is part of the problem. If my wife caught me misappropriating a kitchen implement, then she would beat me half to death.

RS_Jim · 2017-07-21 14:39

hatallica wrote: »

MikeDYur wrote: »

Ok got it, there is no half-life.

Actually, half-life is part of the problem. If my wife caught me misappropriating a kitchen implement, then she would beat me half to death.

Would that not be "half-life"

hatallica · 2017-07-21 15:47

RS_Jim wrote: »

Would that not be "half-life"

To the optimist, yes.

hmlittle59 · 2017-07-26 02:56

Hello All,
OK, I guess I have been really living under a rock!!! Looking on YouTube.com about re-flow ovens and one thing lead to another. I did not know that Hot Air Guns are under $100.00. Looked on my wife's Amazon and there are all different kinds. WOW!!! When I was in manufacturing years ago I thought they cost $700. or more. I even saw a re-flow oven for under $300. This alone could have save me tons of time.
There is way to many for me to read and decide from and all that I did read seem to just repeat. Has any one bought one/two or three from Amazon and how is it holding up. The EEblog did a review on the 858D and it seem to pass the mustard. I've watched over 5 YouTube videos and they all look simple enough. Plenty of board to test on and burn up before starting on the real thing. I have at lease 10 PBasic 48 IC's that I could remove and put on my New and Improved PCB with the voltage comparator IC and divider circuit I just got tuned in and working, see attached and rate PLEASE. NOTE: It is the DUAL chip and both side are balanced...Same readings on the O'Scope. Adjustments may still be needed at the Base of the Transistor 330 ohms - to - ???. Voltage is now at 880mv for Q turn-on.

SO: Help with....
1) Good/decent Hot Air/re-work station...$100. range
2) Rate the attached Voltage Divider circuit.
*Someone here told me to switch from the Dual Voltage comparator that I could (NOT) get to working correctly to a newer version. Thanks.

Thanks to all

EDIT:
oops...forgot to attach and used the BOE and a BS2 to get the Comparator circuit laidout and test code working.

Tried to EDIT and attach my (converted to Bitmap) image of the Schematic, but do not see a way....HELP..

hmlittle59 · 2017-07-26 03:13

Ok,
Maybe you can not attach to a edited file????

But here is the Voltage Divider and Comparator Chip circuit...
my bad

Thanks again.