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Laser Enhanced Ultrasonic Chip Wirebonding

IP.com Disclosure Number: IPCOM000107496D
Original Publication Date: 1992-Feb-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 1 page(s) / 64K

Publishing Venue

IBM

Abstract

Disclosed is a method to enhance wirebonding reliability by assisting ultrasonic energy with laser energy heating. One specific application targeted by the disclosure is the ChipOn-Board (COB) application which requires ULTRASONIC bonding of the wire from a pad on the chip to a pad on the epoxy card. This wirebonding operation is highly automated and it is capable of bonding rates of the order of 5 wires per second. The problem is the erratic reliability of the wedge bonding at the card side caused by the low energy coupling to pads on a soft substrate (epoxy card). Under these conditions the tip is unable to generate consistently adequate levels of heat needed to form strong wirebonds.

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Laser Enhanced Ultrasonic Chip Wirebonding

      Disclosed is a method to enhance wirebonding reliability by
assisting ultrasonic energy with laser energy heating. One specific
application targeted by the disclosure is the ChipOn-Board (COB)
application which requires ULTRASONIC bonding of the wire from a pad
on the chip to a pad on the epoxy card.  This wirebonding operation
is highly automated and it is capable of bonding rates of the order
of 5 wires per second. The problem is the erratic reliability of the
wedge bonding at the card side caused by the low energy coupling to
pads on a soft substrate (epoxy card).  Under these conditions the
tip is unable to generate consistently adequate levels of heat needed
to form strong wirebonds.

      To solve the bonding reliability problem we have modified the
existing chip wirebonding method adding laser pulse heating of the
tip during ultrasonic bonding. The laser beam is focused on the
bottom of the tip by a focusing lens (Figure 1). The laser heat pulse
is to be applied simultaneously with the ultrasonic pulse during the
bonding cycle.   This is accomplished by triggering the laser pulse
by a signal emitted by the bonder at the onset of the ultrasonic
energy pulse.  Similarly, the laser pulse can be terminated at the
end of the bonding cycle.  If necessary time delays (start and/or
end) of the laser pulse in relation to the ultrasonic pulse can be
easily programmed in the interface box communicating the bonder w...