What is a Bonding Tool Called Capillary?

The industry of bonding tools is a very specialized industry and very few knows about what is the nomenclature of the said tool. I was once asked by a technician what is a capillary. He thought is was a small glass tube used in blood testing. On my ten years of employment on a bonding tool manufacturers, I’m very familiar of the design of capillaries but not very well on applications. I mean how it is used to bond integrated circuits. To familiarize you on the cross-section of a simple tip of a capillary drawing, see sketch below ( Fig. 1):

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Fig. 1 – Nomenclature of a Simple Capillary Cross Section

The dimension is actually microscopic (in microns or thousands of an inch) but what you see in the sketch is magnified approximately 200 times. The standard material used is ceramic but there are other materials used too like ruby. Gold wire with the diameter as small as our hair comes out of the hole then the tip of the wire is exposed to microwave and turns into a molten ball, similar to a lead wire when you touch the tip of the soldering gun that forms a small ball of lead (See Fig. 2). Then the capillary will push the ball into the surface of the silicon die which instantly bond the wire that creates a mashed ball. Then it will connect the silicon die to the lead frame (see Fig. 3).

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Fig. 2 – How a Capillary Bonds Gold Wire

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Fig. 3 – Gold Wires Connecting to Lead Frames


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