Reflow parts launching.
Reflow parts launching.
(OP)
After my hideous oven runaway I've got things back to where they were with a new ramp and soak controller that plots on the screen and all that stuff. Fine.
What isn't fine is that the same old problem is back. A lot of boards I do are about 4 x 2 or 4 x 3". I use 0603 parts wherever I can but naturally I have to use 0805 and 1206 etc for either power dissipation needs or cost (big C values in small packages are expensive).
These bigger than 0603 parts have a penchant for bailing out. It's been so consistent that the policy (grating as it is) is to not even bother placing 1206 or larger parts because almost all of them fly. Now I'm seeing a lot of 0805 parts fly too, probably about %50. Hunting down the flyers and relocating them is painfully time consuming.
Looked at a board today thru a microscope and had the feeling I was looking at reconnaissance photos after an extensive bombing run thru a small town.
First crack at trying to logic this, it would seem like the paste has absorbed water that is flashing to steam and launching victims. So I changed the profile to soak at 50C for a while before proceeding. No real improvement was seen.
I've heard to fix this you need to "sprint from the start really fast to the peak". I haven't tried this because it seems like it would increase a rapid vaporization launching problem. On the last 10 boards I ran 3 boards, 3 boards, 2 boards, and 2 boards, and there was a marked reduction in flyers, perhaps by half on the 2 board runs. Not an insubstantial improvement! The difference would be that the temperature can probably move a bit faster on 2 board runs so maybe faster temp ramping has something to it.
Of course when you get down to tiny things that are overwhelmed by forces like capillary action it can all get 'unexpected'.
I use http://www.chipquik.com/datasheets/SMD4300SNL10.pdf
paste.
We often take three days to complete placement so the paste is out for a while, however we don't really see a launched part difference between 5 hours and 72 hours.
Does anyone have suggestions.
Keith Cress
kcress - http://www.flaminsystems.com
What isn't fine is that the same old problem is back. A lot of boards I do are about 4 x 2 or 4 x 3". I use 0603 parts wherever I can but naturally I have to use 0805 and 1206 etc for either power dissipation needs or cost (big C values in small packages are expensive).
These bigger than 0603 parts have a penchant for bailing out. It's been so consistent that the policy (grating as it is) is to not even bother placing 1206 or larger parts because almost all of them fly. Now I'm seeing a lot of 0805 parts fly too, probably about %50. Hunting down the flyers and relocating them is painfully time consuming.
Looked at a board today thru a microscope and had the feeling I was looking at reconnaissance photos after an extensive bombing run thru a small town.
First crack at trying to logic this, it would seem like the paste has absorbed water that is flashing to steam and launching victims. So I changed the profile to soak at 50C for a while before proceeding. No real improvement was seen.
I've heard to fix this you need to "sprint from the start really fast to the peak". I haven't tried this because it seems like it would increase a rapid vaporization launching problem. On the last 10 boards I ran 3 boards, 3 boards, 2 boards, and 2 boards, and there was a marked reduction in flyers, perhaps by half on the 2 board runs. Not an insubstantial improvement! The difference would be that the temperature can probably move a bit faster on 2 board runs so maybe faster temp ramping has something to it.
Of course when you get down to tiny things that are overwhelmed by forces like capillary action it can all get 'unexpected'.
I use http://www.chipquik.com/datasheets/SMD4300SNL10.pdf
paste.
We often take three days to complete placement so the paste is out for a while, however we don't really see a launched part difference between 5 hours and 72 hours.
Does anyone have suggestions.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Reflow parts launching.
You've got some kind of little roller conveyor in there, right?
Make sure the sections are aligned and the rollers are rolling, so the boards don't get jostled.
... out of ideas.
Mike Halloran
Pembroke Pines, FL, USA
RE: Reflow parts launching.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Reflow parts launching.
As in, maybe enough airflow velocity over the boards to lift a component, or propel it sideways on a slippery pool of molten solder?
Mike Halloran
Pembroke Pines, FL, USA
RE: Reflow parts launching.
Are the components truly "popping" off, or are they merely tombstoning? Popping off would mean trapped moisture (as in, inside the component)... any moisture in the paste would slowly evaporate and dissipate rather than explode. Tombstoning would mean improper laydown of the paste or incorrectly designed pads.
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Reflow parts launching.
TTFN
I can do absolutely anything. I'm an expert!
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: Reflow parts launching.
What is the relative humidity in your shop?
Have you contacted the folks at Chip Quik?
They may know exactly what the cause is.
How are you with this advice from the Data Sheet?
Refrigerate at 3-8°C (37-46°F).
Do not freeze. Allow 4 hours for solder paste to reach an operating temperature of 20-25°C (68-77°F) before use.
How is your temperature controlled?
Is your air flow uniform?
Are you pre-cleaning your boards?
How about some one board test runs with shortened and extended ramp times?
Is it possible that you are getting temperature over-shooting that is not seen by you instrumentation due to thermal lag of your instrumentation?
Look at the whole process, not just the flux.
Good luck!
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Reflow parts launching.
RE: Reflow parts launching.
Are these parts marked with a MSL level?
Obviously the "professionals" have baking/storage/dessicant procedures,etc.. that must be maintained so as a "toaster reflow" user that kind of handling/baking procedures are just as important..
even the flux..
Are you storing in a fridge?
If so are you allowing 4 or so hours after the paste is removed from the fridge,etc..
I'd try baking all the parts on your next run just to check.. Baking info should be in J-STD-033 I think..
RE: Reflow parts launching.
Yes, the components are LEAVING. No tombstoning. The parts end up inches from their placements. Often remaining in the oven or landing on other boards.
IR; Pictures won't help as you'd see just an area with missing 0805 components in a neighborhood of intact 0603 parts. Like all the apartments got hit. :/
Bill;
Humidity ~ typically 60%
Paste generally kept at about 60F sealed. It's a syringe.
Toaster oven - no airflow at all, so yes, it's uniform. :)
No not precleaned. Boards are generally brand spanking new out of desiccant packaged bags. But it doesn't change the results if the board is ancient dirty laying around fingerprinted handled.
Process is slow enough that a small diameter T/C can run rings around it.
btrue; Whoa, that's out-of-the-box thinking. There are two radiant rods across the bottom just outside the area the boards span. They are shielded with metal U-channels with a hundred slits in them and are about an inch below the boards. There's nothing really magnetic about the subject ceramic based components though. Could be inducing voltages though most boards these included are almost completely covered with solid ground planes.
mcgyvr; Generally only the IC plastic-molded-onto-leadframes type parts seem to have industry "moisture issues" and my (possibly wrong) understanding is that the entire issue is about those parts exploding due to trapped steam, which of course, is not the issue here. All the leaded parts behave impeccably.
The paste is normally kept in a thermally massive insulated container at floor level in the work space, hence the 60F, unless it won't be needed for more than a week at which time it is refrigerated. There has been no detectable difference between right out of the overnight shipped cold bag verse paste that has sat out for 4 summer months. Same launching either way. Old paste will however cause an increase in more subtle aspects like minor tombstoning will occur. Perhaps 3 components out of 500 instead of 1 part in 500.
Thanks all for your ideas.
I'm going to run a board today. I'll let you know the results.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Reflow parts launching.
TTFN
I can do absolutely anything. I'm an expert!
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: Reflow parts launching.
RE: Reflow parts launching.
I used a very bright flashlight and a lens out of a (retired) bench magnifier and stood in front of the oven door focused on the rows and rows of 0805s. Glancing to the left out the door I could see the large temp display on my office comp. I watched expecting problems around the steam temp 100C. Then 120C. Then 140C 180 200 220 225!! Nada. Not one single flyer. Clearly a very short screen time is effective. In the past probably the quickest screentime was 4 hours, which still gets you flyers.
Seems to me we're seeing moisture absorption. So I will try a very extended drying dwell in the future to see if multi-day screens can be tamed. It'll have to be once I'm well though. :/ hack hack wheeze (It sounds like I've inhaled a harmonica)
Keith Cress
kcress - http://www.flaminsystems.com
RE: Reflow parts launching.
That sounds like a good idea.
Sorry about the wheezing. There's been a bug going around our area; congestion, headaches, body aches, I'm still OK but my 3 out of 5 of my family have been sick.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Reflow parts launching.
It takes a long time to place and check those little guy's, I wonder if using a dehumidifier just in that room would help.
RE: Reflow parts launching.
The space is air leaky like a sieve because it's built as a steel structure out of corrugated steel. Even though my office is 'finished' I literally feel gusts of wind coming from window areas. This pays off with stinky events. LOL
However my placement table is almost a closed space and with very little work I could make it nearly (if not air tight) air dead. Then I could keep it loaded with desiccant when doing a run. I will figure out how to do this.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Reflow parts launching.
Mike Halloran
Pembroke Pines, FL, USA
RE: Reflow parts launching.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Reflow parts launching.
RE: Reflow parts launching.
I have a gallon of industrial compressed air desiccant doing nothing. I figured out today that I can place a typical plastic storage bin upside down over in-process boards sitting in the stuffing table on their static mat. I can set a tray of desiccant in with them. Not only should this prevent moisture absorption I expect it should draw out any absorbed moisture that's gone into the paste. When assembly recommences the plastic bin can be removed the desiccant placed in it and the lid installed to prevent the desiccant from 'doing the room' pointlessly. The desiccant turns red when saturated and can be baked back to electric-blue ready.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Reflow parts launching.
Mike Halloran
Pembroke Pines, FL, USA
RE: Reflow parts launching.
B.E.
You are judged not by what you know, but by what you can do.
RE: Reflow parts launching.
Typical regen dryer: http://www.airdryers.com/air-dryers/vsa.html
But if you just need dry enough air for a shop and the air needs to be just dryer than the local immediate dew point the refrigerated ones work really reliably and don't have a lot of problems with contaminants that a regenerative desiccant unit would hate.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Reflow parts launching.
Z
RE: Reflow parts launching.
Keith Cress
kcress - http://www.flaminsystems.com