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I saw this as a package type for an attiny microcontroller in the digikey catalog. I'm pretty sure that "QFN" stands for Quad Flat No leads. However, I'm not sure what prefixed "WF" means. Is there a standard reference that would have this information?

Eraticus
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2 Answers2

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Funny, ATMEL doesn't use WFQFN as a label. That attiny85 has a 20m1 package, which is based on the JEDEC MO-220 MLP, Otherwise known as QFN. At most, they reference it as WQFN, not WF.

And the W in WQFN stands for Very Very Thin (0.75mm in height). As opposed to VQFN, which is Very Thin (0.9mm). UQFN being the newest and thinest at this time (0.5mm).

Alternatively, WQFN and and UQFN are also known as TQFN and UTQFN. Depends on the manufacturer.

Passerby
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  • Yes. ATMEL does not even give land patterns for their chips, and does not describe this particular chip as QFN. The label WFQFN is from the digikey catalog.http://www.digikey.com/product-detail/en/ATTINY85-20MU/ATTINY85-20MU-ND/1245919 Since the chip is 0.75mm thick, your explanation of the acronym also seems correct. – Eraticus Oct 31 '13 at 01:55
  • @Eraticus according to Atmel, since they stick to official Jedec standard industry footprints, they don't provide them. http://support.atmel.com/bin/customer.exe?=&action=viewKbEntry&id=116 Other manufacturers tend to have proprietary packages or variations though. – Passerby Oct 31 '13 at 02:03
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Seems to stand for wettable flank. I believe it means the pads wrap up the sides of the chip a bit so the solder can stick to the side of the pins as well as the bottom.

http://www.intersil.com/content/dam/Intersil/documents/fn83/fn8354.pdf

Amend that; it has to do with the shape of the pad. This document from Freescale Semiconductor mentions wettable flanks. It seems that the end of the pads are dimpled during manufacturing so that the final solder joints are easier to inspect.

https://www.farnell.com/datasheets/1853246.pdf

Community
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alex.forencich
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  • That explanation make sense from the image in the catalog: http://media.digikey.com/Renders/Atmel%20Renders/20-QFN-PC.jpg – Eraticus Oct 31 '13 at 00:10
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    Actually that's a standard QFN. If you lok at the appnote I linked, it shows some pictures of what the dimpled pads look like. They always wrap around to the sides. On a normal QFN, they have a square corner. On a WF QFN, a small dimple is added right on the edge so that the solder is pulled upwards. – alex.forencich Oct 31 '13 at 00:29
  • Except the ATtiny85 datasheet package drawing shows no sign of Wettable Flanks, nor does the ATmel QFN mounting guide http://www.atmel.com/images/doc8583.pdf – Passerby Oct 31 '13 at 01:54
  • @Passerby OP asked about WFQFN and when I answered there was no mention of the specific part. You're right that the Atmel chip does not seem to be WFQFN, though. It's likely digikey had another data entry error. – alex.forencich Oct 31 '13 at 05:36