Wire bonding has traveled far and wide from the early days of semiconductor manufacturing. That’s when wire bonding was used to connect a chip to a package, like the early, early days of dual-in-line (DIP) ceramic and plastic packaging. But today, wire bonding is being performed in microelectronics cleanrooms in PCB assembly and manufacturing areas.
As shown in Fig. 1, Wire bonding is now connecting a bare die onto a substrate or a rigid-flex circuit in a variety of PCB applications, including IoT and wearables, as well as industrial, mil/aero, and medical electronics. The top requirement here is for reliability and ruggedness.
There are 10 key principles that must be adhered to with pinpoint accuracy in assembly and manufacturing so that wire bonding maintains high reliability. Some are interrelated. However, as standalones, each one is critical.
Check out our blog appearing in IoT Agenda for more details.
In the meantime, here’s the rundown on half dozen of those major principles.
- First and foremost, metallization is extremely important. This means creating a bond between the substrate on the PCB and the die. If the surfaces aren’t clean and oxidized, the strength of the wire bond is highly questionable.
- Different nuances are associated with gold, aluminum, copper, and silver wiring. There must be assurances from wire bonding and PCB assembly experts that using a certain type of wire is compatible with a given application.
- Flip chips or chip scale packaging (CSP) must be mounted properly on the board for wire bonding to work and be securely attached before wire bonding starts. If not, the created joint will not be reliable. When pull strength testing is applied to the wire bonded joint, the wire will come off.
- Virtually all wire bonding requires a fixture to lay the substrate flat. Knowledge and expertise are critical here for precisely creating those fixtures for ultra-fine devices to be wire bonded. Tolerances must be extremely tight to properly hold the substrate before it gets wire bonded.
- An experienced programmer is required to deal with an array of wire bonding variables. That programmer must also be savvy enough to perform wire bonding accurately, calculate and verify bonding strengths, bond integrity, and bond placement before doing the actual bonds.
- Get assurances the EMS Provider knows to perform plasma cleaning using argon gas to clean substrates, as needed. The surface of those substrates must be 100 percent defect and oxidation free for perfect wire bonding.
Wire bonding has two categories, wedge and ball bonding, each distinctively different. Each requires separate and different sets of systems and temperatures for wire bonding operations. For wedge bonding, either aluminum or gold are typically used. For ball bonding, gold wiring is typically used. Wedge and ball bonding also differ in the way the wire bond is made on the chip side. The bond is made resembling a gold ball, while the end of the wire is in a wedge-shape for wedge bonding.