Will the world end if I ignore this?

Go To Last Post
15 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Bought some micros cheap for hobby use.  This was on the bag.

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Watch the bag seal - he might bite!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

This is for happy use, not hobby smiley

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Only if you intend to put them through a reflow oven. If left out, they can get excess moisture inside which vaporizes in a reflow oven cracking the case. There is a protocol for baking out the extra moisture if they've been out of the bag too long.

 

I've never had trouble with it when I use a frypan to solder.

The largest known prime number: 282589933-1

It's easy to stop breaking the 10th commandment! Break the 8th instead. 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks much for the explanation.  If this is a problem, why do most chips come without such warnings and packaging?  I think I've only seen such warnings, and received such packaging, a couple of times in my life.  Is is just that the standard tape-and-reel packaging, with each chip in it's little pod, is moisture-proof?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I think that it has something to do with the package (e.g. IC) construction. It seems more prevalent with larger sizes or pin-counts.

 

Then, again, I have gotten warnings like that on parts from one of the major distributors where it seems to be a pro-forma warning for anything SMT. Resistors, maybe?

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Not seen it for passives, but of a batch of components I got this morning from Digikey, the 74HC27 are sealed in a moisture pack with one of those cobalt moisture detection cards in (from the feel of it; I can't see through the packing!) while the 74HC4075 and 74HC574 are in normal packs... go figure. And the pin headers and sockets are just in ziplock bags.

 

On other occasions, pretty much all of the active parts have been sealed. As pointed out above, this is only really significant if you're machine building - and generally if things are sealed, they're also on a pick'n'place reel. So I wonder if it's just that?

 

Neil

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I wonder also why I ever get "loose" SMD ICs (payed out in flat antistatic cardboard boxes)?  How did they come from the factory?  Certainly not loose in bags.  

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

technically each and every component that can take on moisture should have this warning. That includes capacitors and resistors.

As assembly houses should have this as common practice the warning labels might be not standard there.

You should be able to see on youtube what happens if you do not 'bake' components before you put them on a PCB and put them through a reflow oven.

I have seen some movies from the people who interface with our china production were they had a camera pointed at the oven and a series of ' bad'  devices in different stages ( IIRC they had been deliberately moisturized for the video)

The end result was that we had chips that initially looked good, even all production testing was OK, but they would fail later as the top of the processor had cracked open just a little bit, but badly damaging the bonding wires which only showed up after time as again moisture would get in and do its thing.

To chips that were decapitated and the entire top was badly damaged, thus clearly visible damage. In which case they pointed out in the video that also the assembly line had to be cleaned .

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Leds also tend to be fairly susceptible - they go off like popcorn.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I wonder if I am too cynical in thinking this may simply be an arse covering exercise. You receive the chips, you build them into a product, several units fail. You pursue the chip vendor for refund/compensation because of "faulty chips" and they say "did you adhere 100% to the advice on the label?" knowing full well that no one ever adheres 100% to it - it's the ultimate "get out clause"! cheeky

 

BTW if the devices really are "moisture sensitive" then do they suddenly stop being "moisture sensitive" when mounted on a PCB or can we all expect our chips to go all "soggy" after a while?

Last Edited: Fri. Aug 2, 2019 - 08:17 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Cliff - it's a real problem. For us hobbyists that hand solder parts, it's not an issue. When it does become an issue is when you use an oven to reflow the solder - the sharp rise in temperature causes the moisture to turn to steam with bad results. To combat this you can bake the devices at a low temperature for X hours to evaporate the moisture.  Its covered by a JEDEC standard!

 

Pretty well what meslomp said in #9.

 

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

kk6gm wrote:
How did they come from the factory?  Certainly not loose in bags.
Very typically tape-and-reel or plastic trays though some PCBA manufacturers can receive bags (empty the bag into a tray and optical recognition by the pick-and-place machine to identify the parts)

Bags are more from distributors who pull the parts from reels and/or trays; a BOM can be "kitted" by a distributor into a bag.

The plastic tray may or may not be bake-able.

MSL 1 is easier for PCBA manufacturers.

 

https://www.avrfreaks.net/forum/uc3-legacy#comment-2736096 (part numbers ending in R are reels, T for trays, automotive is Z before R or T)

 

edit :

tapes from reels at the sides with trays on the platform with the PCB :

Pick & Place Video - Rapid PCB

 

"Dare to be naïve." - Buckminster Fuller

Last Edited: Fri. Aug 2, 2019 - 04:15 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Oddly enough, had a grump at Farnell yesterday regarding packing: they sent a handful of 144 pin surface mount microcontrollers just between expanded polystyrene and in a standard ziploc bag; they arrived, half having escaped from the polystyrene and as a result having their legs bent.

 

We would have expected ideally they would arrive in the manufacturer's antistatic pick'n'place trays, but at the very least in antistatic foam boxes. We were not happy... but Farnell's held their hands up and are shipping new parts.

 

Neil

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

clawson wrote:

I wonder if I am too cynical in thinking this may simply be an arse covering exercise. You receive the chips, you build them into a product, several units fail. You pursue the chip vendor for refund/compensation because of "faulty chips" and they say "did you adhere 100% to the advice on the label?" knowing full well that no one ever adheres 100% to it - it's the ultimate "get out clause"! cheeky

 

BTW if the devices really are "moisture sensitive" then do they suddenly stop being "moisture sensitive" when mounted on a PCB or can we all expect our chips to go all "soggy" after a while?

 

Yea, they'll take on moisture, but you usually don't put a finished product back in a reflow oven. I have fixed a couple faulty devices by frying them again.

The largest known prime number: 282589933-1

It's easy to stop breaking the 10th commandment! Break the 8th instead.