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2013-03-15 by Steven Hodge
I realize this is off-AVR topic, but why the sudden(?) proliferation of putting parts in moisture-sealed packaging (e.g., by Digi-Key and Mouser), when they were previously not so packaged? Must the accompanying Threat of Dire Doom be taken seriously if limits are exceeded? Why does it seem limited to just SMT devices and not DIP? Thanks, Steve
2013-03-15 by Tim Mitchell
----Original Message----
From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf Of Steven Hodge Sent: 15 March 2013 16:02 To: AVR-Chat@yahoogroups.com Subject: [AVR-Chat] moisture-sealed packaging > I realize this is off-AVR topic, but why the sudden(?) > proliferation of putting parts in moisture-sealed > packaging (e.g., by Digi-Key and Mouser), when they were > previously not so packaged? Must the accompanying Threat > of Dire Doom be taken seriously if limits are exceeded? > Why does it seem > limited to just SMT devices and not DIP? > I'm not sure why they have suddenly started, but the reason it's done for SMT not DIP is because of the oven soldering that is used with SMT devices - they can explode/crack when put through the oven due to moisture boiling to steam inside the device. I have seen it happen quite a few times with LED's, but never with any other devices. The parts are sealed from the manufacturer, but once they open the pack and start chopping a few off the reel, the reeled parts start absorbing moisture. I can only assume they then re-seal the pack and remove all the moist air, otherwise the packaging to the end user is pointless. -- Tim Mitchell
2013-03-18 by Steven Hodge
So, Tim, in my case I use solder paste, a pre-heater and a hot air nozzle from a rework station. Might it be safe to assume there is less of a problem than with an oven? Steve
From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf Of Tim Mitchell Sent: Friday, March 15, 2013 9:18 AM To: AVR-Chat@yahoogroups.com Subject: RE: [AVR-Chat] moisture-sealed packaging ----Original Message---- From: AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com> [mailto:AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com> ] On Behalf Of Steven Hodge Sent: 15 March 2013 16:02 To: AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com> Subject: [AVR-Chat] moisture-sealed packaging > I realize this is off-AVR topic, but why the sudden(?) > proliferation of putting parts in moisture-sealed > packaging (e.g., by Digi-Key and Mouser), when they were > previously not so packaged? Must the accompanying Threat > of Dire Doom be taken seriously if limits are exceeded? > Why does it seem > limited to just SMT devices and not DIP? > I'm not sure why they have suddenly started, but the reason it's done for SMT not DIP is because of the oven soldering that is used with SMT devices - they can explode/crack when put through the oven due to moisture boiling to steam inside the device. I have seen it happen quite a few times with LED's, but never with any other devices. The parts are sealed from the manufacturer, but once they open the pack and start chopping a few off the reel, the reeled parts start absorbing moisture. I can only assume they then re-seal the pack and remove all the moist air, otherwise the packaging to the end user is pointless. -- Tim Mitchell [Non-text portions of this message have been removed]
2013-03-18 by Tim Mitchell
----Original Message----
From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf Of Steven Hodge Sent: 18 March 2013 14:17 To: AVR-Chat@yahoogroups.com Subject: RE: [AVR-Chat] moisture-sealed packaging > So, Tim, in my case I use solder paste, a pre-heater and > a hot air nozzle > from a rework station. Might it be safe to assume there > is less of a > problem than with an oven? Steve > Who knows, like I say I've only ever had a problem with LEDs. In those you can see bubbles of steam forming inside them when you heat them up, and this seems to destroy/disconnect the bond wires. -- Tim Mitchell
2013-03-18 by Steven Hodge
Thanks, I think I'll just keep them in their packages, re-sealed as best I can, but otherwise ignore the warnings.
From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf Of Tim Mitchell Sent: Monday, March 18, 2013 8:49 AM To: AVR-Chat@yahoogroups.com Subject: RE: [AVR-Chat] moisture-sealed packaging ----Original Message---- From: AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com> [mailto:AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com> ] On Behalf Of Steven Hodge Sent: 18 March 2013 14:17 To: AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com> Subject: RE: [AVR-Chat] moisture-sealed packaging > So, Tim, in my case I use solder paste, a pre-heater and > a hot air nozzle > from a rework station. Might it be safe to assume there > is less of a > problem than with an oven? Steve > Who knows, like I say I've only ever had a problem with LEDs. In those you can see bubbles of steam forming inside them when you heat them up, and this seems to destroy/disconnect the bond wires. -- Tim Mitchell [Non-text portions of this message have been removed]
2013-03-18 by bayramdavies
--- In AVR-Chat@yahoogroups.com, "Steven Hodge" <steve@...> wrote: > Thanks, I think I'll just keep them in > their packages, re-sealed as best I > can, but otherwise ignore the warnings. For what it's worth, that's what I've always done and it doesn't seem to have got me into any trouble. I use a modified toaster oven for reflow of tin/lead and occasionally lead-free solder paste. Graham.
2013-03-18 by Bob Paddock
On Fri, Mar 15, 2013 at 12:01 PM, Steven Hodge <steve@terrafirma.us> wrote: > > > > I realize this is off-AVR topic, but why the sudden(?) proliferation of > putting parts in moisture-sealed packaging (e.g., by Digi-Key and Mouser), > when they were previously not so packaged? Must the accompanying Threat of > Dire Doom be taken seriously if limits are exceeded? Why does it seem > limited to just SMT devices and not DIP? Don't know why things have change, other than perhaps a better awareness of the issue. What you want to find is the MSL rating in the datasheet for your respective part. http://en.wikipedia.org/wiki/Moisture_Sensitivity_Level MSL 6 - Mandatory Bake before use MSL 5A - 24 hours MSL 5 - 48 hours MSL 4 - 72 hours MSL 3 - 168 hours MSL 2A - 4 weeks MSL 2 - 1 year MSL 1 - Unlimited In some cases the MSL is not in the datasheet but in some secondary file related to packages and/or quality reports. Some manufacturer report it as the empty package so they don't put it in a part datasheet, and you have to dig for it. -- http://blog.softwaresafety.net/ http://www.designer-iii.com/ http://www.wearablesmartsensors.com/
2013-03-18 by Jim Wagner
SMT is more sensitive that through-hole because the body of the part is subject to greater temperature change and much more rapidly. For example, in SMT (in a reflow machine), the whole body if the part is raised to nearly the solder melting temperature. But through hole, even on a wave machine the body does not get nearly so hot. The whole issue water is that absorbed into the epoxy resin of the package. Yes, it really happens. If you heat it slowly, the water vaporizes and works its way out. If you heat it quickly, the water does not have a chance to diffuse out, and expands in place, leading to part failures and sometimes ruptures. Some epoxy packages have cavities where the die is; these are even worse because there is an open but enclosed volume in which the water vapor can expand (explosively). If you are machine soldering SMT parts, that have a significant part of the device volume as epoxy, and the parts were not packaged in a humidity barrier package, I would prebake no matter what. Without looking it up, which anyone who is concerned should do, I would heat to 50C for a good hour, then solder within a pretty short time. One should also point out the obvious: this is much more significant in, say, Louisiana, Alabama, or Florida in the summer, than any time of the year in Colorado or Utah. Jim Wagner Oregon Research Electronics
----- Original Message ----- From: "Bob Paddock" <bob.paddock@gmail.com> To: AVR-Chat@yahoogroups.com Sent: Monday, March 18, 2013 1:34:05 PM Subject: Re: [AVR-Chat] moisture-sealed packaging On Fri, Mar 15, 2013 at 12:01 PM, Steven Hodge < steve@terrafirma.us > wrote: > > > > I realize this is off-AVR topic, but why the sudden(?) proliferation of > putting parts in moisture-sealed packaging (e.g., by Digi-Key and Mouser), > when they were previously not so packaged? Must the accompanying Threat of > Dire Doom be taken seriously if limits are exceeded? Why does it seem > limited to just SMT devices and not DIP? Don't know why things have change, other than perhaps a better awareness of the issue. What you want to find is the MSL rating in the datasheet for your respective part. http://en.wikipedia.org/wiki/Moisture_Sensitivity_Level MSL 6 - Mandatory Bake before use MSL 5A - 24 hours MSL 5 - 48 hours MSL 4 - 72 hours MSL 3 - 168 hours MSL 2A - 4 weeks MSL 2 - 1 year MSL 1 - Unlimited In some cases the MSL is not in the datasheet but in some secondary file related to packages and/or quality reports. Some manufacturer report it as the empty package so they don't put it in a part datasheet, and you have to dig for it. -- http://blog.softwaresafety.net/ http://www.designer-iii.com/ http://www.wearablesmartsensors.com/ [Non-text portions of this message have been removed]