Digikey humidity-control packaging of QPF Propeller chips

Greg Glenn

I have ordered two Propeller chips from Digikey over the past 3 months, both of them QFP configuration.· Both times they were delivered in not only static-shield bags but also humidity-control bags with silical gel dessicant and a cardboard humidity indicator that turns from blue to pink as humidity levels rise.·· It says that if humidity is over a certain level, the component should be baked.··

Is this just overly cautious packaging by Digikey, or do the QFP propellers really have some sensitivity to humidity?

Phil Pilgrim (PhiPi)

The sensitivity is due to moisture intrusion along the lead/package interface. Theoretically, moisture trapped in this interface could vaporize rapidly when heated during soldering, causing the packaging material to fracture. Baking drives out the moisture more gently ahead of the soldering process. Personally, in all the SMT packages I've soldered, I've never had this issue crop up.

-Phil

Leon

It can cause a problem with reflow soldering. Manual soldering is OK.

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Leon Heller
Amateur radio callsign: G1HSM

Cluso99

It is to do with commercial assembly. For your own purposes you may ignore this. I am sure there is plenty of info on the web and wiki if you want further info.

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Rayman

I think Digikey prepackages a lot of low quantity stuff so they can pull it off the shelf fast. I imagine they put the dessicant there because it could be on the shelf for years before being sold...

The ones I get from Digikey come in cut tape. I don't remember if there was dessicant or not...

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Jack Buffington

Has anyone ever had problems with parts that were packed in desiccant when working with a hot air rework station or using the electric griddle soldering method? I have been doing those recently but have been really careful to not let the parts' humidity get too high. It wouldn't kill me if I lost a part now and again because of some humidity but if I were to lose one or four or something like that, it would be a disaster.


-Jack

WBA Consulting

MSL parts are unfortunately dear to me as it is a real issue during reflow soldering, especially with higher end components. The MSL handling process at work is one of my current pojects to re-vamp into an easier I deal with a particular LED that is an MSL4 class part which means it can only be out of packaging for 24 hours. (or out of a humidity controlled environment, IE[noparse]:o[/noparse]ven) The assembly that it is used on is ran in lots of 2,000 which takes us about 4 days to run. (can you see the predicament?) The LEDs are kept in an oven ANY time they are not being used on the machine to prevent moisture issues during reflow.

As PhiPi already mentioned, it has to do with moisture trapped inside the package that creates a popcorn effect during reflow. With manual soldering, the component will not see temperatures that cause the popcorning so it is not an issue. As far as toaster oven reflow or griddle methods, you may or may not see issues, but keep in mind that "popcorning" cannot always be seen (the worst cases split open the top of the package hence the popcorning nickname) and may not always completely kill a device. It may only render a few pins useless, degrade the speed of a device, shorten the lifespan, or etc, etc.

I don't see an MSL level listed for the QFN prop, but many QFNs of the same size I deal with our MSL 3, which means it can be out of packaging for 168 hours before baking is recommended. However, that also depends on the package material Parallax is using and whether or not it is moisture sensitive.

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Andrew Williams
WBA Consulting
WBA-TH1M Sensirion SHT11 Module
Special Olympics Polar Bear Plunge, Mar 20, 2010

Tracy Allen

When I order parts in trays directly from Parallax, they always arrive vacuum packed in a black vapor barrier bag with desiccant, and I leave it that way when I send it to the assembler. But I don't recall any specific discussion of moisture sensitivity. It is good practice I guess. Some other parts, such as Atmel dataflash memories, arrive in humidity control packaging with a control label, stating how long they can be out of the bag before mounting/reflow and that the humidity indicator card in the bag has to show less than 10%RH, otherwise bake at 125 degC for 48 hours.

A friend who worked for HP on high reliability government projects once told me it is almost impossible to avoid micro-cracks, especially along the lead frame, no matter what the soldering method. And that over the long term in extreme environments those cracks can widen like rock layers in Yosemite. That relates to to humidity during soldering but also to stresses induced in the package by non-uniform soldering methods.

Semiconductor packaging materials have improved greatly. Andrew, do you happen to know what materials are on the sensitive list and why they continue to use them if alternatives are available?

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Tracy Allen
www.emesystems.com

WBA Consulting

I can do some digging to get specific materials, but basically any parts that are non-hermetic will have concerns.

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Andrew Williams
WBA Consulting
WBA-TH1M Sensirion SHT11 Module
Special Olympics Polar Bear Plunge, Mar 20, 2010

Unknown

Phil Pilgrim (PhiPi) said...
The sensitivity is due to moisture intrusion along the lead/package interface. Theoretically, moisture trapped in this interface could vaporize rapidly when heated during soldering, causing the packaging material to fracture. Baking drives out the moisture more gently ahead of the soldering process. Personally, in all the SMT packages I've soldered, I've never had this issue crop up.

-Phil

I was trained to replace the quartz bulbs on motion picture projectors and we had to use cotton gloves or do it without touching the bulb because the oil on our hands would cook on the bulb and they would sometimes burn a hole through it or explode due to the difference in atmospheric pressure.