Increase Flex Cycle Life of Flexible Printed Circuit (FPC) Assembly
Name: Douglas Bulmer
Company Name: Miraco, Inc.
Job Title: Vice President of Engineering
Address: 102 Maple Street Manchester, NH 03103
As an industry leader, the customer is constantly pushing the limits of technology to provide
healthcare professionals with the latest products that achieve superior performance.
A non-invasive medical accessory to assist surgeons, dentists, and hygienists with meeting
the needs of patients and improving surgical safety.
Miraco’s customer was experiencing a higher than desired field return rate of their product due to unknown failures. Miraco was tasked with evaluating these returns to determine the root cause and to develop a solution to reduce product failure.
Miraco prides itself on offering state of the art evaluation, analysis, brainstorming, and
cutting-edge solutions to real world problems. All of this is balanced with the need for
reducing costs and lead-times while delivering a high-quality, reliable product. Miraco
enthusiastically accepted the challenge of solving this customer’s product life issue and
integrating it into current production without causing a stockout condition to the market.
Purpose of Project / Technical Challenge:
Miraco’s customer, a leader in the medical industry, developed a product which was a step
above in terms of style and technology compared to its competitors’ products while
maintaining a competitive market price. Unfortunately, the product was not meeting
reliability expectations and needed to outperform competitive offerings which were available
to medical professionals.
The customer tasked Miraco with reviewing the current design and performing failure
analysis on returned customer product. The goal was to significantly improve the life of the
product with minimal or no impact to the overall assembly cost, product class, and tooling.
In addition, the customer’s intent was to introduce the revised product to the market in less than six months.
Miraco developed test methods which were designed to push the product to the point of
failure while simulating normal working conditions in order to determine root cause(s). To
accomplish this, Miraco designed and built a custom flex cycle life testing machine which
accurately simulated the worst case flexing conditions for every day human use. The
machine was used to exercise the prototypes while monitoring the electrical resistance and
number of cycles to failure.
The testing and analysis demonstrated that the failures were isolated to a specific portion of
the FPC where it passed through a hinge joint which was subjected to flexural fatigue. It
was determined that the current FPC was not designed to handle the worst case bending
conditions that the product could experience during day to day use resulting in lower than
desired flex cycle life.
Utilizing state of the art software, Miraco designed several prototype options which would
help reduce stress introduced to the thin copper layers of the FPC. The thought process
included focusing on strain relief, bend isolation, stress reduction, copper grain direction, and
proper material stack-up which would maximize flex cycle life. The prototypes were then
tested to verify improvements to the flex cycle life.
Miraco engineering demonstrated that by revising the routing of the FPC through the hinge
and modifying the circuit layout to reduce stress, that flex cycle life increased by nearly 10
times therefore providing a much higher quality product to the customer. This was all
accomplished without affecting the selling price or having to modify any tooling related to the
Benefits / Business Case:
Customer Benefit: Miraco’s customer now offers the market a product which outperforms
and outlasts its previous product. Product appearance and pricing has not changed, while
the reliability has improved, and the customer’s name brand reputation been maintained.
Miraco Benefit: Miraco has gained the customer’s confidence on this product and has been
offered the opportunity to not only become the primary / sole source of the FPC, but also is
in discussions of completing the box-build of the completed product.