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 [URL unfurl="true"]http://www.chipquik.com/datasheets/SMD4300SNL10.pdf[/url]
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 -
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 [URL unfurl="true"]http://www.chipquik.com/datasheets/SMD4300SNL10.pdf[/url]
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 -
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