Rapid Prototyping of High Density, Fine-Line Flex Circuits

Smaller devices require smaller circuits, and in many cases, those circuits must be flexible enough to bend during use. Unlike rigid printed circuit boards, flexible circuits carry their components on flexible plastic substrates that allow movement during use.

Designing and building a high-density flex circuit that can withstand extreme temperatures, hold up under repeated use, and have lines and spaces as small as 25μm isn’t the easiest of tasks. And, accomplishing this task in 20 days or less with lot sizes as small as one unit requires a tremendous amount of experience and teamwork.

While there are many things any flex circuit manufacturer can do to build high density, fine-line flexible circuits, we have boiled the process down to five essential ingredients.

1. Engineer-to-Engineer-to Engineer Rapport

Flex circuit design is ideally a collaborative experience between an experienced flex circuit team and the customer.

Whereas the customer may arrive with a 6-layer design, we may reduce it to four or even two layers if it reduces the size and cost, improves reliability, and reduces design and manufacturing time without compromising the objectives of the circuit.

There are a tremendous number of variables and options when designing and building a flex circuit. For this reason, establishing a good rapport between your engineers and the flex circuit manufacturer’s engineers is fundamental to your overall success.

To facilitate a collaborative atmosphere, we’ll do the following within 24 hours of receiving an idea, concept or design from a customer:

  1. Distribute the specifications to our flex experts, laser micromachining experts, thin film experts, and others as necessary.
  2. Review the specifications internally and explore existing processes that may be fine-tuned for the given application.
  3. Bring the customer onto a “Web-based” conference call in which we can visually discuss ideas, alternatives and processes.

We’ve found that this kind of collaborative effort is the only way to quickly turn an idea into a working prototype.

2. Establish Consistency in Flex Circuit Design.

One of the first things we’ll do with a new project is to assign a single flex circuit engineer to work the project from design through manufacturing.

While some flex circuit manufacturers may find it more cost-effective to “release” a design to production, we’ve learned that the consistency and focus that a single point of contact brings to the project is paramount to the success of the project.

This single point of contact ensures that all processes are included and are consistent through each stage of the development. We use a system known as “Lean Manufacturing” or “Lean Thinking” that includes “Value Stream Maps.

The value stream maps enables the engineer assigned to the project to optimize each step and maintain a level of consistency that is unachievable through normal design and manufacturing methodologies.

3. A Multi-Disciplinary Approach to Flexible Circuits

One thing that’s unique about MicroConnex is that all our engineers are cross-trained in the three key disciplines required to design and manufacture 1 mil trace and space high-density flex circuits.

The three key disciplines are:

  • Flex circuit design
    Laser micromachining and laser drilling
    Thin film sputtering

We can produce flex circuits with lines and spaces down to 25μm on very thin layers of Kapton and other materials. Thinner copper layers make it easier to produce fine-pitch circuits and higher-quality polyimide substrates, while our thin film sputtering process helps us to create an all-gold circuit that won’t corrode inside the human body.

What enables us to work with a variety of materials at a fine level is a multi-disciplinary approach to the design and manufacture of flex circuits. High-density, fine-pitch flex circuits require knowledge and experience in all three disciplines, so every project will include one or more engineers with expertise in each discipline.

Then, because the engineers are cross-trained, an expert in one area can easily communicate to the other engineers’ ideas or specific design suggestions. Valuable input is not lost because an engineer is too tightly focused on one discipline.

We’ve learned that it is beyond the ability of any single engineer to be a master of all the disciplines necessary to achieve the unique and rigorous goals of cutting edge flex circuit design and manufacturing. Thus, a multi-disciplinary approach gives us the best of everything.

4. All for One and One for All

Communication only works when the people involved in the conversation have a vested interest in the outcome.

While it may be simple to use project management software to ensure that everyone on the “team” receives project updates and information, it’s not so easy to ensure each person’s active involvement in the project.

Although we have a single point of contact for the consistency of each project, the outcome of the project is in everyone’s lap. Consequently, communication is not simply a one-way affair between a “project lead” and the rest of the team. Even if a team member is on the periphery of the project, his or her input is encouraged at each step of the way.

By assigning overall “ownership” of the outcome of a project to all engineers on the team, we ensure that communication remains open and relevant to the success of the project.

5. Will it work?

Even engineers can get caught up in the thrill of the chase, especially when working with lines and spaces 25μm and smaller.

We always conduct a final feasibility review, both internally and with the customer, before the prototype is built. This final step ensures that what we’re building meets all initial design criteria, as well as additional design criteria developed in collaboration with the customer.


What we’ve described is part process and part culture. A company can’t force a multi-disciplinary approach that involves personal responsibility for the outcome of every project, but it can develop a culture in which these things become the norm.

When working with a flex circuit manufacturer, especially with high-density fine-pitch circuits on difficult substrates, it is important to understand how they develop the circuit. The process contributes more toward a successful project than the expertise of any one engineer.

Read more about Flex Circuits and Laser Micromachining from MicroConnex.