1. Field of the Invention
The present invention relates generally to solder masks for use on carrier substrates and, more particularly, to solder masks that are configured to prevent excess adhesive material from contacting or covering terminals of carrier substrates. In addition, the present invention relates to carrier substrates including such solder masks and to semiconductor device assemblies and packages including the carrier substrates. The present invention also relates to methods for designing solder masks to be used on carrier substrates, to methods for forming solder masks on carrier substrates, and to methods for connecting semiconductor devices to carrier substrates.
2. Background of Related Art
Circuit boards and other carrier substrates have long been employed to establish electrical communication between bond pads of semiconductor dice and other electronic components, including those carried by the circuit board and components that are external to the circuit board.
Conventionally, relatively small circuit boards have been used to package one or more semiconductor dice, which protects the dice and provides a semiconductor device package that includes a standardized connection pattern, regardless of the arrangement of bond pads of each semiconductor die of such a package. These circuit boards are often referred to in the art as “interposers.” In the state of the art, the dimensions of interposers are approaching the corresponding dimensions of the semiconductor dice to be secured thereto, with the result being a continuous decrease in the sizes of semiconductor device packages, many of which are so-called “chip-scale packages” exhibiting dimensions that are the same as or only slightly larger than those of the die thereof.
Nonetheless, when conventional wire bonding processes are used to electrically connect bond pads of a semiconductor die to corresponding contacts, or terminals, of an interposer to which the semiconductor die is back bonded, the terminals of the interposer must be positioned outside of the outer periphery of the semiconductor die. This requirement prevents a reduction in the size of these interposers to dimensions that are substantially the same as those of the semiconductor die to be secured thereto and carried thereby.
Moreover, in order to securely attach a semiconductor die to the circuit board, it is typically desirable that a sufficient amount of adhesive material be used to form a confluent adhesive layer adjacent to the back side of the semiconductor die and a fillet around the entire outer periphery of the semiconductor die. Some excess adhesive material is typically required to adhere the semiconductor die and the circuit board to one another in this manner. When excess adhesive material is used, however, some of the adhesive material may flow outward from the semiconductor die, beyond the desired location for a fillet, and contaminate the connection surfaces of adjacent terminals, which are located at the same elevation as or just above a surface of the circuit board. If the connection surfaces of the terminals become contaminated in this manner, intermediate conductive elements, such as bond wires, may not adhere thereto or form an effective electrical connection, which may ultimately reduce the reliability of the packaged semiconductor device, or cause electrical shorting and failure of the packaged semiconductor device.
Larger circuit boards, such as so-called “motherboards” and the substrates of so-called “plug-and-play” devices or cards, may be configured to carry a plurality of semiconductor devices. As with interposers, the trend with such larger circuit boards is also toward ever-decreasing sizes and ever-increasing densities. Consequently, contamination of the connection surfaces of terminals by adhesive material is increasingly encountered when semiconductor devices are assembled with larger circuit boards.
Solder masks are often used on circuit boards to facilitate the formation of solder balls or bumps on selected terminals of the circuit boards while protecting other features thereof and preventing solder from wetting and adhering to other features of the circuit board. The solder masks that are used on circuit boards are typically fabricated from photoresists, using known photolithography processes. These solder masks may be left in place while semiconductor devices and other components are secured and electrically connected to the circuit board. Thus, a semiconductor device may be secured to a solder mask which is, in turn, secured to the circuit board to which the semiconductor device is to be electrically connected.
When conventional solder masks are used on conventional circuit boards, a portion of the adhesive material that secures a semiconductor device to the solder mask may still flow laterally outward, beyond the outer periphery of the semiconductor device and onto connection surfaces of the adjacent terminals of the circuit board.
Some solder masks have been configured with recesses to receive some of the excess adhesive material. Nonetheless, these recesses typically do not have great enough volumes to contain all of the excess adhesive material that is forced from beneath a semiconductor device as the semiconductor device is secured to the solder mask and, thus, to the circuit board. Consequently, the terminals of circuit boards are typically spaced a sufficient distance away from the location at which the outer periphery of a semiconductor device to be secured to the circuit board is to be positioned that the connection surfaces thereof will not be contaminated by adhesive material. Such positioning of the terminals undesirably requires that the circuit board include additional real estate, which prevents a reduction in the dimensions of the circuit board.
The inventors are not aware of any carrier substrates or solder masks therefor that are configured to prevent adhesive material from flowing onto the connection surfaces of the carrier substrate terminals while reducing the dimensions of the carrier substrate.