Direct micro-joining of flexible printed circuit and metal electrode by pulsed Nd: YAG laser

Mohd Idris Shah Ismail, Yasuhiro Okamoto, Akira Okada, Yoshiyuki Uno, Kentaro Ueoka

Research output: Contribution to journalArticle

14 Citations (Scopus)


Laser micro-welding has proven to be a very successful tool for micro-joining in the electrical and electronic industries, where the miniaturization, the high strength and the high heat resistance are constantly requested. Recently, a flexible printed circuit (FPC) is expected as a new connection technology between electrical conductors according to the improvements of reliability and controllability with the diversification of the design concept. In this technology, it is required to weld a several tens μm thickness of FPC and a several hundreds μm thickness of metal electrode. This material combination accompanies the difficulty to control the welding phenomenon due to the differences of thermal property and heat capacity. As a good alternative, laser micro-welding has advantages of non-contact tool, low heat distortion and consistent weld integrity. In this study, the overlap welding of thin copper circuit on a polyimide film and a thick brass electrode was experimentally and numerically investigated by using a pulsed Nd:YAG laser. In addition, the shearing stress of overlap welding was evaluated with and without the control of pulse waveform, which can provide a well-directed controlling of the heat input with high energy density. The results showed that a porosity was observed as the major weld defect in the welding process without a pulse control. However, the appropriate controlled laser pulse configuration of micro-welding could remove the weld defects in the molten zone, improve the weld penetration stability and increase the weld strength. The potential benefits of controlled pulse waveform were discussed for the direct laser micro-welding process. It is clarified that the direct laser micro-welding of a thin copper circuit on a polyimide film and a thick brass electrode could be successfully achieved by appropriate controlled pulse waveform and heat input.

Original languageEnglish
Pages (from-to)321-329
Number of pages9
JournalInternational Journal of Precision Engineering and Manufacturing
Issue number3
Publication statusPublished - Mar 2012



  • Copper
  • Overlap welding
  • Post-heating
  • Pre-heating
  • Pulse waveform
  • Rest time

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Industrial and Manufacturing Engineering
  • Mechanical Engineering

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