We’ve come to the end of my New Year’s Resolutions for 2020. Before we dive deeper into the exciting new capabilities to be found in the 17.4 release, though, I’d like to address a question I hear from new users all the time. That question being why, when placing a die component from the library or the front-end tool, is its default attachment type and orientation flip-chip chip-down?

Give me just a minute here and allow me to explain. Hopefully, you’ll agree that the way the tool behaves is both logical and consistent. I’ll even give you some guidance on ways to impact this default behavior if you need to.

Why Flip-Chip?

This is the easier of the two parts of the question. Why is the default attachment type for a die added from the library or front-end flip-chip? A die can be mounted as a flip-chip in any package layout cross-section. These dies, when attached to the top or bottom surfaces, have their pads instantiated directly on the outermost conductor layer (TOP_COND/BOT_COND or SURFACE/BASE, usually).  

A wire bond attach die, on the other hand, is mounted with its pins facing *away* from the substrate surface. Its electrical connections into the substrate take the form of bond wires spanning from the die pad down to a bond finger or power/ground ring. Even in the case of a slot-bond package, where the wire bond die is mounted chip-down on the top substrate and bonded through a slot to fingers on the backside, the die pins themselves still exist on the die stack layer above the top surface. The pins are not eligible for direct wire or via connection from the substrate.

Because wire bond dies require at least one die stack layer in the cross-section, they cannot be legally placed in any substrate that lacks these layers. To maintain consistent behavior across all designs, regardless of the contents of the layer stack-up, flip-chip was selected as the default attachment type.  

Why Chip-Down?

A flip-chip die is most commonly mounted to the top of the package substrate. It could be placed on the top conductor layer, inside an open/closed cavity referenced from the top, or even placed higher up in a die stack on this side of the design. It is uncommon (but certainly not unheard of!) to mount the flip-chip to the backside of the package, in the center of the BGA ball pattern.

When mounted on the top of the package, a flip-chip must be flipped over from its manufactured orientation in the IC design domain. Because it’s flipped, its orientation is chip-down, and that forms the total default orientation for the component when it first goes onto your cursor in commands like place manual.

I’ve Placed My Components. How Do I Set Orientation and Attachment?

Once you have placed your components where you want them in the design, use the die stack editor one-stop-shop to set all their orientation and attachment types. Here, you can also identify any groups of dies which should be placed into cavities (open OR closed), moved components to the other side of the substrate, or even move an entire stack as a single unit.

As you change the attachment, orientation, mounting layer, and die stack attributes, the graphics in the upper-right corner will give you a real-time illustration of what the stack looks like. This will help you immediately determine issues that count result in assembly problems including missing spacers, interposers, and excessive overhangs.  

Can I Change the Default Attachment and Orientation for My Parts?

You sure can! If you work primarily with wire bond dies, then you may want to default all chips to the wire-bond attachment. This can be done with a one-time environment variable setting in your user preferences. The variable is ICP_DEFAULT_ATTACH_WIREBOND. When this is set, all dies will default to a wire bond attach type, even if there are no die stack layers in the cross-section.

Before you’ll be able to place these dies with place manual, you WILL need to make sure to add at least one die stack type layer to the stack-up! Your dies will default to the most common orientation for wire-bond parts, which is chip-up (unmirrored) automatically when you use this variable.

If, on the other hand, you are driving your components from the front-end tools through a netrev flow, you can set properties in the schematic to tell the layout tool what each individual component definition’s suggested attachment type/orientation are. The two properties you will need are:

1. DIE_ATTACH_TYPE – “WIREBOND” or “FLIPCHIP”

2. DIE_ATTACH_ORIENTATION – “CHIPUP” or “CHIPDOWN”

With these placed on the component definitions, your schematic owner can drive this information directly into the layout for the designer. The same advisory applies here as with the user preference. If you have dies that will use a wire bond attachment method, you’ll need at least one die stack type layer in your design before placing them.

Depending on your specific application, hopefully, one of these will permit you to work quickly, and easily, to get all IC components in your design placed accurately with high efficiency. If you run into any troubles, however, contact your customer support team so we can help you get the most out of your tool!