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Let’s talk about wire bonding for a quick minute. Still a favorite for many of you, bonding is a cheap way to connect your die to the top layer of your package (or to a lead frame, if that’s what you’re using). A 3D wire is connected to the pad on your die, then the machine bends the wire to create a curvature through space on its way to the bond finger on your substrate.
Forward and reverse bonds, stitch bonds, ribbon bonds, or bond wires coated in a dielectric material in case they touch—there are many variations on the types of bonds you will see, and even in how you place your components around the substrate to minimize total bond wire length (gold’s not cheap!).
One type of wire bonds that I get asked about from time to time aren’t special in the material they are made of, but rather how they travel through air to get from start to end. Most wires, you see, follow a straight path. Sure, they go up into the air and curve down to the bond finger (assuming you’re not coming up out of a cavity or something fun!). If you were to look straight down at the wire from above, it would look like a straight line from pin to finger.
When filling under the die after bonding with reflow material, the fill material can cause the wires to bend slightly, getting closer to one another along their profile paths.
Or you can, in fact, design your bond wires with curves in their profiles to start, if you’re using the Cadence® SiP tools.
If you are a SiP or APD user, you’ve no doubt seen the wire profile definition form before. It’s been around for a few years, now.
You may NOT have noticed a few fields on this form, however, that let you define profiles that look completely different from those plain, old, point-to-point straight 2D paths. The Hor. Turn field in the grid (last row in the image above) specifies the angle of bend in the horizontal plane for the segment being acted on.
A 45-degree angle, for instance, means this segment turns 45 degrees (counter-clockwise) from the previous segment. In my example, then, the second segment moves 45-degrees counterclockwise while the vector climbs 10 percent of the height over 10 percent of the wire’s length. The third segment (25% of the wire’s length) comes back 5 degrees in the opposite direction, clockwise.
If you’re having trouble making sense of this, the dynamic sample image at the bottom of the page can display your wire from either a side view (the default, showing the vertical height changes along the wire’s length) or from the top-down perspective to show you the bends in the wire horizontally. Whichever segment you’re working on is highlighted with the green box to make it easy to track.
Defining a complex profile like this directly inside of the layout environment not only allows you to get the most accurate image in 3D but also ensures that everything from your Sigrity-using SI engineer to the OLP programmer of the bonding machine know the exact intent of your design. You’ll even know more accurately the total wire length used for each produced package, making sure your cost estimates are as accurate as possible.
Curious what a curved profile like this looks like when applied to a bond wire? Wonder no more, just stay with us. Our example profile’s been assigned to two wires and I took a picture for your viewing pleasure:
Looking from the top of the die out over the wires, you see how the wires bend with each segment but also go up and down. Any wire-to-wire or wire-to-substrate 3D clearance rules you define process all segments for highly accurate distance checks and violation reporting, so you can be sure that your finished part will work as intended.
In the main 2D canvas, SiP shows a simplified 2-point vector for the wire. This might sound like a limitation, but in fact, it is very useful. Your top-down, 2D perspective in the layout shows you only part of the picture. Without access to the vertical height changes, what you see may make you think there is an error that is not truly a problem. For this reason, any time you want to look at the wires, beyond a connectivity path (like a rats nest line), we recommend viewing in 3D. Otherwise, you may make changes to the design that are unnecessary at best, incorrect at worst.
That is a GREAT question! Your bonding machine provider may have certified wire profile definitions available for you (some are provided with SiP itself). And, so long as your changes to the profile inside the profile editor remain within the allowable limits set by the manufacturer, the profile will remain certified and show the vendor’s certification logo in the profile editor form. Deviate too much, however, and you’ll be warned and the profile will be flagged uncertified, meaning you need to validate your geometries with an experience bonding engineer/programmer to be certain.
While we always urge you to verify your design with the bonding engineer up-front before characterizing things in SI/PI tools, if you remain within certified profile limits, you can be confident that your bonding machine will be able to create the wire pattern you’ve defined.
So, if you are worried about bending or just need the extra room that can be afforded using all dimensions at your disposal, give it a shot! Should you need help getting started, a call to your local AE or our customer support experts will get you moving in no time at all!