Screaming Circuits: QFN and DFN


CAD Library or Substitution Issues

We recently ran across an issue out on the shop floor that was most likely due to the components library in the CAD package. A QFN part was sent for this assembly but the land pattern on the board was... Read more

Silver via problems

Here's an interesting via situation that I hadn't heard about until just recently. In these two cases, the engineer has a QFN with a center pad that is required more for grounding then for cooling. Given the lack of criticality,... Read more

Microvias, Blind and Buried Vias

In a few previous posts, here, here and here, for starters, I've discussed the dreaded via in pad and hopefully, given some useful information about what to do if you must put vias in pads. In the image, (A) shows... Read more

Soldermask Via Caps

Today, I'll start with the basics: Soldermask via caps. This isn't the best, but it is the easiest. Almost any board house can pull this one off with a reasonable chance of success. In this example, what we're looking at... Read more

Via in pad methods

Here is another method for dealing with QFN heat slugs with thermal vias. While the best option is to plug the via holes with metal early in the board fab process and then plate over with copper, there are a... Read more

Most parts in place

Mark Rules has made a bit of progress on his tiny motor controller. Someone suggested that he look at a rigid-flex board so that the driver could be wrapped around one of the motors. The idea would be to have... Read more

QFN solder voids

I've written a couple of posts about QFN float problems (here), (here) and (here). There is another problem we run across as well. With larger QFN parts, the opposite problem can occur in the center pad area. When the square... Read more

QFN CAD Libraries

In previous posts (here and here), I've talked about QFN layout issues and solder stencil openings. Here is an example of a the library that follows the component manufacturer's and our recommendations. First step is the copper layer. In this... Read more

QFN solder paste stencil guidelines

To better illustrate the proper way to make your solder paste stencil for QFN parts, as I discussed in the post just before this one, I went to the back room and took a couple of photos of good and... Read more

QFN float be bad

At a recent tradeshow, I received a sample part in a 3 x 3 mm QFN package. While I haven't tried yet, I'm pretty sure that, like a water bug, the part is light enough to float on a water... Read more