Westbond 7476E Status Active Superusers Ivan Penskiy (ipenskiy[at]umd[dot]edu) Important documents and useful links Westbond 7476E user guide Overview Westbond 7476E is a manual ultrasonic wedge wire bonder designed to bond wire leads between contact pads of packages, ICs, and MEMS devices. It is currently set up with 1 mil aluminum wire but can also support gold wire and ribbon (would need to be purchased to use). Location E.A. Fernandez IDEA Factory building 228, Room 3119c. Laser cutter specifications Heated workholder with mechanical clamp 400 watt temperature controller K~1200D DeWeyl vertical deep access bonding tool Reservation Westbond 7476E wire bonder must be reserved before using. The reservation is done using the Google calendar. You will be able to reserve the equipment personally after attending the RAL lab orientation and then following the steps below to gain access to the equipment. Please estimate reservation times (they can be changed after the fact) and limit your reservations to a 6 hour maximum to ensure other users also have access to the system. Video demonstration The following videos demonstrate capabilities and the some aspects of operating Westbond 7476E: Westbond 7476E: Overview Westbond 7476E: Wire threading 101 Video of wedge bonding process Note: these are promotional and instructional videos. They are included for demonstrational purposes only. The details of actual operational procedures in RRL can differ! Important reminders The tooling head can be easily damaged. Be very careful when working around this so as not to break it! Always lower the work holder platform when finished using the wire bonder. This helps to ensure that the next user does not crash the wedge into the work holder when they start. The manipulator provides an 8:1 reduction ratio of your hand motion during bonding. The bond tool must NOT be pushed hard into the bond pad -- only a very light touch is necessary! If you are having significant difficulty re-threading the wedge, contact a superuser for help. Standard operating procedure Preparing die and packages for wirebonding Wirebonder setup Bond buffer and machine settings Wirebonding Shutdown Preparing die and packages for wirebonding: Make sure that your package and dies are clean. Photoresist residue, fingerprints, epoxy, solder flux, and silver paste on surfaces will make bonding difficult if not impossible. Be careful when attaching your die to a package or board. It is easier to keep the bonding pads clean during assembly than it is to remove glue or solder flux after assembly. The most effective way to clean bondable surfaces is with an acetone soak, followed by an acetone rinse, an alcohol rinse, a de-ionized water rinse and nitrogen dry. Do not let the surfaces dry between rinses. For polymeric substrates, DO NOT use acetone or alcohol. Use only a mild detergent and a lot of DI water to rinse the substrate before bonding. Always wear clean gloves when preparing packages for wire bonding and during bonding. In general, aluminum wire has a shelf life of 6 months in air. After that, enough surface oxide can build up on the wire to impede bonding. Never handle the spool without wearing gloves — contaminants can reduce shelf life. The metal bond pad on your device/substrate must also be oxide free and the metal must adhere well to the substrate. If your device has metal adhesion problems, do not expect to be able to get good wire bonds. If you are having difficulty getting wires to stick to the package metallization, try lightly scrubbing the metal surface with sharp tweezers to expose fresh metal and bond to this surface. Wire bond pad design: A pad thickness of at least 800 nm is recommended for good bonds. In general you will want the wire bond pad width to be at least four times the wire diameter and at least 400 um long. That is, you'll want a 125x400 um bond pad for 1 mil wire. Bond pads can be smaller for gold wire bonds. Pad pitch is also important. Given a reasonably small bonding wedge, an aggressive pitch would be 60-70 um, but it is recommended to design a much higher pitch. Recommended methods for die attachment to a package: Use a small drop of photoresist to glue your die to the package and bake at 120C for 5 minutes. The die can be removed using an acetone soak. Use silver paste to glue the die, then bake at 120C for 10 min. It will form a permanent and conductive bond. Use fast-dry epoxy (~5 min) to glue the die. It can form a permanent bond at room temperature. Wirebonder setup: Push the "Power" button to switch ON the main power. The LCD light will turn on. Select the proper work holder for the package that you are using. Proper fixture of your die (chip) and package are very important! The die must be rigidly mounted to the package so that ultrasonic energy from the bonding wedge can be transmitted efficiently to the die. This means that using adhesive tape or grease to temporarily mount a die to a package will probably cause failed wire bonds. Set the work holder height. Once you have selected the proper work holder for your substrate, make sure that the work holder table is all the way down before placing the work holder onto the table. This is needed to prevent damage to the ultrasonic transducer by accidentally running the work holder into the wedge. Once you have done this, carefully place the work holder onto the table. Bring the wedge to a location above the package that represents the lowest bond height that will be made. Very slowly lower the tool to its lowest position using the manipulator, making sure that you do not crash the wedge into the work holder or package! Once you've reached the lowest position that the wedge will travel with the manipulator, slowly raise the table by turning the front knob on the table clockwise so that the lowest plane on the package to be bonded is about 0.025 inches above the lowest point that the wedge can reach. Bond buffer and machine settings: Wirebonding: Shutdown: Gaining access to equipment Preparation Scheduling training Preparation: Read the user guide for Westbond 7476E. Read the Standard operating procedure section. Prepare die and package for bonding. Scheduling training: Once you are confident in the topics from the previous section, email the lab manager (Ivan Penskiy, ipenskiy[at]umd[dot]edu) to schedule training. Usually it takes 2-3 sessions to become an authorized user.