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Author Topic: TQFP cautions, what's the deal?  (Read 2225 times)

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Offline jsmokerTopic starter

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TQFP cautions, what's the deal?
« on: June 18, 2007, 02:02:18 PM »
I've been working with PDIPs and SIOCs but a new project required a chip with 16 analogue inputs so I had to move to the TQFP footprint.  I thought, no big deal, just more leads, but when it came, it was in a vacuum sealed pouch with a level 3 caution on it saying it's moisture sensitive. That it has to be mounted in a certain time after being opened and other whatnots.  What's this about?  Is it just moisture sensitive for the soldering process, because of heat expansion or something?  Is it always moisture sensitive?

-Jason

Offline JonHylands

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Re: TQFP cautions, what's the deal?
« Reply #1 on: June 18, 2007, 02:33:50 PM »
What it means is you shouldn't take it out of the sealed package, and then leave it sitting on your workbench for a week before you decide to solder it.

The main difference between TQFP and SOIC is not only the number of pins, its also the pin pitch. SOIC is typically 0.050" pitch (pin spacing), and QFP is often 0.65mm (which is about 0.025") or 0.8mm (which is a little bigger).

The chips I use for my Bioloid boards are MLF format, which have 0.5mm pitch. I use a stencil to apply solder paste, and then bake it in my reflow oven.

- Jon

Offline jsmokerTopic starter

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Re: TQFP cautions, what's the deal?
« Reply #2 on: June 19, 2007, 12:20:28 PM »
I figured it meant use it right away after opening, but I was looking for a more technical answer to reason behind it.  Like I said, I assume that it due to thermal expansion and tolerance changes with moisture, but that's only an assumption.  Would the internal joints fail with thermal expansion due to moisture since tolerances are smaller?  How would moisture effect the expansion?

Offline Admin

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Re: TQFP cautions, what's the deal?
« Reply #3 on: June 19, 2007, 07:22:48 PM »
Quote
In designing packing materialsand methodologies, AMD is sen-sitive to the susceptibility of somepackages to moisture-induced damage. The risk of this is great-est when using plastic encapsulation materials, as plastic is naturally permeable to moisture.The moisture in the package will increase or decrease to reach therelative humidity (RH) of the surrounding environment. Controlling the moisture level in the package body is, therefore, critical in reducing the risk of moisture-induced damage. Such damage may include internal delamination of the package materials from the die and/or lead-frame/substrate or internal cracks. External cracking may also occur when components are exposed to the high temperatures and steep temperature gradients used in reflow board assembly techniques. Moisture in the package rapidly heats and vaporizes and, if there is sufficient steam due to the moisture in the package having reached a critical level, it will fracture the package to escape. This phenomenon is known as the "popcorn effect."


taken from:
http://www.amd.com/us-en/assets/content_type/DownloadableAssets/12drypack.pdf

 


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