With so many variables, troubleshooting wire bond programs can be tricky. The tips that follow will make the process a bit easier.

Tip 1: Confirm that the wire bonder's setup is correct.

a) Install a new wire bonding tool and set screw. If not available, make sure the old bonding tool is the correct part number for the wire size being bonded. Under a microscope, at 10X minimum, inspect the tool and set screw to see if it is worn out or dirty. Reinstall the tool and seat the set screw to the manufacturer recommended setting with a torque wrench. Test the ultrasonics; if the ultrasonics are tuned and working properly, proceed with the setup.

b) Install a new spool of wire. If new wire is not available, confirm the wire in the old spool is the correct size and alloy composition. Make sure the wire is not dirty, damaged, or spooled incorrectly. Verify the wire feeds smoothly through to the bond tool.

c) Load the secured copy of the wire bond program into the wire bonder. Always keep a copy of the wire bond program in a secured area away from the production floor. You can easily reinstall the program if the production copy becomes corrupt.

d) Using a calibrated thermometer, verify the heated stage is the correct temperature. A thermosonic process, gold wire bonding typically requires the product be heated to 150 ºC.

e) Using a setup sample, evaluate the program for repeatability and resulting bond strengths.

Tip 2: Bond surfaces must be clean, smooth, and free of contaminates. Use cleaning solvents to flush away contaminates from bond surfaces. Plasma cleaning will remove micro contaminates but in most cases will not remove debris or other macro contaminates. Oxygen plasma will remove organic contaminates. However, to remove inorganic oxides, you will have to use argon gas or a mix of argon and oxygen gas. The plasma from these gases will remove both organic and inorganic contaminates. Measure the effectiveness of plasma cleaning by placing a drop of DI water on the bond surface and visually examining the contact angle of the water drop. A high contact angle indicates surface contamination. A low contact angle, where the water drop spreads over the bond surface, indicates a clean surface.

Tip 3: The product must be rigidly held. If the product moves during wire bonding, ultrasonic energy is lost and the bond will not form completely. Check your work holder, or make sure the tool is clamping the part rigidly before the wire bonding operation starts. The clamping should be repeatable. You may have to put a time delay in your program to allow the clamped part to settle before starting the wire bonding process.

Tip 4: Check for consistent and symmetrical free-air-balls. The diameter should be approximately 1.5 times the wire diameter (See figure 6-1).

Tip 5: Adjust the ultrasonics, force, and time. Change one parameter at a time, as changing all the parameters at once will make it impossible to determine which change has the most impact on improving the wire bond.

Tip 6: Replace the wire bond tool with a different lot number of the same tool, or use an equivalent tool from a different supplier.

Tip 7: Replace the wire with a different lot number from the same supplier, or use an equivalent wire from a different supplier.

Tip 8: Finally, check the equipment calibration, the bond head mechanisms, and the operation of the machine.

With good controls on incoming materials, dependable wire bond process control checks, and regular equipment maintenance and calibration, the wire bonding operation will run defects of less than 100 ppm.