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I'm implementing the NXP TDA19988 HDMI transmitter IC in one of my projects and I am currently in the PCB design stage. I am building my component library and when I came across this part I wasn't sure how to proceed. I am familiar with standard 64-pin QFNs. However, this one seems to have additional "pads" on the bottom, besides the normal electrical connections:

enter image description here

Unless I overlooked it, they do not seem to be mentioned in the datasheet. Are these simply extensions of the ground plane/pad on the bottom of the IC? My suspicion is that they are acting as a reference plane for the internal bond wires leading to the electrical pads to provide controlled-impedance, in which case I assume I need to have them connected to ground. Is there a specific land pattern that I should follow for these sorts of packages? The land pattern I have is the SOT804-2 (vs. the SOT804-4 I'm really looking for) and can be found on page 3 of this document:

https://www.nxp.com/docs/en/package-information/SOT804-2.pdf

EDIT:

Since apparently I wasn't being clear enough with my question, here it is in a concise, readable format:

Where can I find the recommended land pattern for the SOT802-4 64-pin HVQFN package used for this device?

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  • \$\begingroup\$ OK, it seems that your question has confused both @TimWescott and I. Exactly what part of the land pattern are you asking about? Are you confused about what physical land pattern you should use, about the connections to the lands, or something else entirely? \$\endgroup\$ – Elliot Alderson Jun 17 at 0:07
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    \$\begingroup\$ @ElliotAlderson Specifically I'm asking about the discrete exposed pads extending between the center ground pad and the electrical connections, and whether or not special lands need to be added to the footprint for them to solder to. My guess was that they're just supposed to sit on top of the ground pad in the footprint, in which case no special footprint is necessary \$\endgroup\$ – DerStrom8 Jun 17 at 0:20
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    \$\begingroup\$ 1. It's odd that nxp.com has no product page for this part number. (for example, to find their product page with links to the correct package drawings). 2. The datasheet says that the TDA19988 is available in an SOT804-4 package, but you found the drawing for the SOT804-2. There's likely some differences that you can't be sure about until you find the correct drawing. 3. I think it's most likely the mystery pads are just part of the leadframe connecting to the usual pads. \$\endgroup\$ – The Photon Jun 17 at 0:34
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    \$\begingroup\$ You could ohm out a sample to see what the mystery pads are actually connected to. But really, if you're not a big enough account to get attention from an NXP applications engineer, this part looks like a risky choice. \$\endgroup\$ – The Photon Jun 17 at 0:35
  • \$\begingroup\$ I'll probably email NXP from my work address tomorrow and see if I can get a reply \$\endgroup\$ – DerStrom8 Jun 17 at 1:20
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This might be the drawing for SOT804-4, which you are looking for. The land pattern is on p.3 .
The second row isn't soldered to the board, if I'm reading the drawing correctly.

I'm guessing, each oblique pad in the second row is connected to the pin on the outer row. So, the second row would be signals, not all grounds. If you have the an IC in your hands, you could check continuity.

p.s. I wonder what's the rationale for this odd QFN, and why a typical QFN didn't cut it.

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  • \$\begingroup\$ This is extremely helpful. Seeing the correct package in the same spec as a land pattern makes me much more confident. Much appreciated! \$\endgroup\$ – DerStrom8 Jun 17 at 10:43
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Page 3 of that document gives you a land pattern. You don't have to guess.

In general, data sheets give you recommended PCB layouts, or refer you to documents (like that one) that give it to you.

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  • \$\begingroup\$ There is nothing in the actual part datasheet that points me to the linked document, that's just a document I found for a package with the same description. I have often come across package "variants" that use different land patterns and was wondering if the same is true for this particular part, hence my question. \$\endgroup\$ – DerStrom8 Jun 16 at 23:11
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    \$\begingroup\$ If I had to guess I'd guess that you want those funny diagonal things to sit over solder mask. But I would ask NXP -- if you're buying enough of them then NXP should help. Or see if they have an evaluation board that includes Gerbers, and use what they did. \$\endgroup\$ – TimWescott Jun 17 at 0:15
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    \$\begingroup\$ This is a personal project, and thus volume will be very low. I may still contact NXP though, if I can't find an answer elsewhere. There used to be an eval board but it appears to be obsolete, and I'm not finding the gerbers for it \$\endgroup\$ – DerStrom8 Jun 17 at 0:30
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I think the information you are looking for is at the end of Table 3 in the datasheet. This table lists all of the pin connections for the QFN package, as well as the exposed die pad.

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  • \$\begingroup\$ Yes, that is true, but that doesn't mean the footprint doesn't include additional copper. That is why I'm looking for the actual footprint for this package, just to confirm that the additional "pads" are (or are not) connected to ground or some other signal. \$\endgroup\$ – DerStrom8 Jun 17 at 1:22

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