How do you go about testing your IC or package substrate when it comes to physical endurance? For many of us, a daisy chain test package is a common option. With practical uses including extreme environmental and temperature testing scenarios, a daisy chain test device can provide you with valuable feedback for a much lower cost versus using known good dies. They make testing easier, as checking for a broken connection in a daisy chain can be done very quickly and efficiently. How do you go about creating one?

If you’re reading this, you are likely a user of the Cadence® SiP and APD package layout tools. The SiP tool provides you with a daisy chain tool to transform a pattern of pins into a routed daisy chain with a few clicks of the mouse – regardless of whether you’re trying to create just the package side of the chain or both the package and IC sides. Keep reading to learn more about this simple, yet powerful, tool in place to make sure you have the most reliable, durable final product possible.

Linking Your Chains

The Daisy Chain command, found in the Route menu, brings up a simple set of parameters in the options tab for you. Have you not done so already, you may need to enable it from your user preferences command. As it is still technically in beta as we wait for more of you to try it out, you'll need to set the "icp_daisy_chain_beta" variable (IC_Packaging/Early_Adopter folder) and restart the tool before proceeding. To make this a regular feature, please use it and provide your input!

If you haven’t already created pin pairs for the connections, the first few options will allow you to do this and to control the names given to the created nets.

The middle section allows you to describe how to group pins. While horizontal and vertical are the basic direction styles, diagonal links are also available. A final option, based on the pin numbers, allows you to do creative patterning for complex, fully custom situations. We will dive into that a little later.

Which corner you want the tool to start from, how many pins are in each link in the chain, and whether to start staggered (begin with the second loop in the chain, instead of the first) allow you to define how the links form and whether this component is the start of the chain or an interior component, as you always want the first link in the chain to be accessible to the outside world.

The tool can create simple routed connections between the pin pairs to save you an additional step. This is on by default and is controlled by the final pair of fields on the form.

How does this all come together to create a chain in just a few seconds and mouse clicks? A picture, as they say, is worth a thousand words. Nothing beats a good example!

Routed Results

The image below shows one side (in this case, the package substrate side) of connections generated by the daisy chain tool using the parameters from our earlier options form. The tool has created the necessary pin pairs and added a routed connection between the alternating pairs, starting from the top left corner and moving horizontally. 

The other side of the pattern can be generated in the same manner. Since the die pads line up with their bump pads on the package, the only adjustment you need to finish the complete chain is to flip the “start pin staggered” option to on (and perhaps adjust the trace width if you like). Hit go a second time and you’re finished!

The final result, then, shows both sides of the chain. By using the same color for both, I can see the long, unbroken horizontal lines that move across the pattern, alternating on the package layer and the die layer.

Additional Considerations

If you wish, more connections can be quickly made between rows of pins to further lengthen the chain. The tool doesn’t do this automatically for you if you’ve guided it to create only horizontal, vertical, or diagonal pairings.

When you have a bump pattern that has a set of peripheral rings but also a core area of power and ground pins, each area of pins will be daisy-chained separately. The tool will not add a long trace between the peripheral and core to combine them. We leave the decision on where to make that connection between the sets to you, based on your testing requirements and concerns. 

Going back to an earlier point about the ability to create both the package and IC side of the chains directly within SiP, this is worth some consideration. For components like flip-chips, which may be mirrored onto the substrate, this gives extra assurance that the final orientation of the patterns will match up when the component is finally mounted. Plus, it looks nice!

Advanced Patterns

How do you drive the tool if you want to minimize the number of chains down to only one, but still want to use the daisy chain tool? Are you out of luck, doing the final steps completely manually? No! The SiP tool includes an integrated symbol editing environment with a host of pin numbering capabilities. Everything from simple alphanumeric grid patterns to spirals and serpentine patterns are standard issue, with interactive renumbering (drag your mouse across a pattern of pins to number them as you touch them) being available for complete customization. 

Once you’ve numbered the pins the way you want them, use the daisy chain tool with a “Pin Number Order” direction and the chain will follow the specified numbering pattern. Repeat the two steps above to generate one side, and then the other, to complete the alternating chain of routed pin pairs and you’re finished!