Stacked Wire-Bond Loops: Special Care Demanded - Nexlogic
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Wire bonding as a central focus for PCB microelectronics manufacturing demands considerable attention as part of the overall PCB hybrid manufacturing. In particular, wire bond loops and their pull strength for reliability and integrity are critically important. Those wire bond loops must be accurately and correctly calculated, formed and executed on the microelectronics manufacturing floor utilizing the proper tools and equipment, as well as highly trained personnel.

That said, even greater attention goes to stacked wire-bond loops. Here, we’re talking about two to three sets of wire bond loops and sometimes even four sets. Each set has different lengths.

These sets of loops crisscross over one another, going on top of one set of wire bonds on top the second, and then going on top of a third. Stacked wire-bond loops, as shown in Fig. 1, pose special microelectronics manufacturing challenges. Therefore, it takes the right equipment and highly trained technicians to accurately perform these stacked wire-bond loops to maintain overall wire bond integrity.

Close attention to wire-bond is one of a trio of factors helping to assure high reliability and integrity. Read our article in SMT007 Magazine for more details. In the meantime, here are some tips and hints to get a more complete understanding.

  • Technicians must ensure wire-bond loops aren’t overly extended when they are performed.
  • Wire loop set crisscrossing creates a series of wire bonds on top of each other resulting in an angle on which the bond is stitched on the pad. The angle has to be accurately calculated and verified.
  • Pad length from the first set of wire bond to the second and third needs to be correctly calculated and verified to create acceptable staggered wire bonding product.
  • Proper PCB or substrate surface finish must be selected at the manufacturing level.
  • Assurances must be made that the amount of nickel, copper, or gold is properly specified in the microelectronics assembly drawings.
  • A physical pull test measurement is the final judge as to wire bond integrity.

There is a companion side associated with maintaining highly disciplined wire bonding reliability and integrity technical procedures. That is PCB hybrid manufacturing engineers and technicians doing the programming for wire bonding stitches and loops must be sufficiently experienced to perform effective and optimal programming of the wire bonder so that optimal length could be achieved and these bonds are sturdy and enduring as specified in the scope of work.