Inductive Coupling Emissions between Bond Wires in Integrated Circuits

Abstract

When making an Integrated Chip, there is a process called contacting or bonding. In this process, the circuit is connected to the capsule. As a result, there is interference between the bond wires through inductive coupling. At higher frequencies, the problem becomes more apparent, which means that the role of frequency in interference should be investigated. By using a bonding machine and making our own measurement prototype, measurements were conducted. Bonding wires on PCB's with different layouts made it possible to investigate differences in interference and coupling. The measurements are also compared with values from a simulated model.
PCB's were manufactured with different spacings for bond wires located on them. Measurements showed a measurable increase in crosstalk as the spacing decreased. Simulations with a model representing the different spacings yielded simulated values which showed a good accordance with measurements. Efforts to limit the coupling were made using two methods. The first method involved using grounded conducting lines beneath the bond wires. These were routed both parallel and perpendicular to the wires. The second method involved copper lines in a similar fashion to the first method, but placed in a way such that an additional bond wire can be placed on them parallel to the existing bond wires, in between them. While the first method had little effect on the coupling between the wires, the second method using a ground wire arrangement was found to be effective. On average, the crosstalk was reduced by 4.50 dB, 4.82 dB, and 6.16 dB on the different PCB's.

Popular Abstract

Many electrical devices contain some sort of Integrated Circuit, or IC. These small chips can operate as timers, oscillators or even CPU's, making them invaluable in many applications. IC's have pushed the boundaries of both performance and space, making it possible to manufacture high-performance devices in compact spaces. IC manufacturers have managed to make IC elements as small as only 10 nm!. Compact dimensions can cause problems however, which becomes apparent when connections to IC's are formed, for instance.

Bond wires are a cost-effective and relatively practical way of forming connections to an IC, making them a popular option for many manufacturers. Compact IC's and a large number of input- and output-connections mean that the spacing between these wires often becomes small. It is then that the problem of coupling between wires manifests itself. Depending on the application, coupling between wires can have a significant deteriorating effect on the performance of chips. Signals sent along one path can leak over to an adjacent path and cause issues, depending on the sensitivity of the chip. Higher frequencies serve to worsen this problem as inductive coupling increases.

In this thesis, forward transmission and crosstalk between bond wires was measured. PCB's, or Printed Circuit Boards, with space for bond wires were manufactured for the purpose of investigating the coupling. Boards with bond wire spacings of 0.15 mm, 0.325 mm, and 0.5 mm were manufactured. In order to investigate possible methods of limiting the inductive coupling, circuits with different limiting arrangements were manufactured. The first method was a simple structure beneath the wires for the purpose of disrupting the magnetic field of the bond wires. The second method involved an additional wire in between to bond wires, which was connected to bond pads in turn connected to a ground. The first method was relatively ineffective in reducing the crosstalk. The latter method showed promise however as the coupling was reduced by several magnitudes.

The phenomena investigated in this thesis can serve to better understand the interference that manifests itself as coupling between bond wires. This is especially important as higher frequency applications are becoming more and more common in electronics. Methods that have been investigated for the purpose of limiting the coupling that occurs has the possibility of aiding in the design of circuits such as RF-frequency Integrated Circuits, or RFIC's. Coupling problems discussed in this thesis is not only limited to RFIC's however. These methods can also be helpful in the design of digital circuits, as signals with short rise- and fall-times can also cause unwanted coupling between bond wires.

• author: Nurdal, Erman and Beldin, Gabriel
• supervisor: Andreas Johansson; Stefan Höst
• organization: Department of Electrical and Information Technology
• course: EITL01 20192
• year: 2019
• type: M2 - Bachelor Degree
• subject: Technology and Engineering
• keywords: Interference, Coupling, Induction, Bond Wire, Integrated Circuit
• report number: LU/LTH-EIT 2020-739
• language: English
• id: 8998930
• date added to LUP: 2020-01-13 14:49:06
• date last changed: 2020-01-13 14:49:06