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    Material Selection for High-Speed PCBs

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  • Implementing Flash Memory in PCB Design

    Implementing Flash Memory in PCB Design

    Routing flash has EMI implications.   READ MORE...

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Flexperts

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Category: Flexperts

Rotating flex circuits are buildable, but will require additional considerations.

I have an application where I need to make an electrical connection to a rotating shaft. The shaft rotates approximately 180° in each direction. Can a flex circuit wrapped around the shaft like a clock spring accomplish this? Are there any guidelines to follow or ways to predict life expectancy?

While clock spring flex designs are not super common, they are certainly not rare either. I have had multiple successful clock spring flex designs over the years. Most of these initial designs probably would not have performed as desired in the “as received from customer” state, but with a little bit of guidance we tweaked the designs and they all ended up performing well.

Read more: Clock Spring Flex Designs

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Category: Flexperts

Flex and rigid-flex can handle all via types – with some considerations.

We have talked before about vias, but some situations can trip you up in flex and rigid-flex, and some tricks can be exploited to overcome them. When it comes to rigid-flex and flex, keep in mind these things.

To start – yes, you can put a microvia in a flex laminate. In fact, I would argue that in an apples-to-apples comparison, a microvia in flex laminate will be more reliable than in rigid reinforced laminate. There are a few reasons for this. One is, the thin flex cores enable low aspect ratio vias, which has been proven to improve reliability.

Flex microvias can also take advantage of certain material attributes. Because flex laminate is a homogenous film without any reinforcement, it lasers very cleanly and the side walls of the hole are uniform. Without any glass weave, the laser cuts through the dielectric evenly, reaching the target pad at the same time with the same power level across the pad. This results in a consistent target pad surface for plating.

Read more: Via Viability

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Category: Flexperts

Proper design and handling can minimize the risk of rips.

I have a potential new application for a flexible circuit for use in an inspection device. The flexible circuit will see some light pulling and tugging forces when extracted. Should I be concerned the circuit may be prone to tearing? If so, are there different materials that can be used that will not tear?

The short answer is yes; flex circuits can tear if not properly designed or handled. You did not mention the number of layers or the thickness, so I will assume that your application is only one or two layers and is on the thin side. As the layer count goes up, so does the thickness, and therefore the strength and tear resistance. Once a flex is four-plus layers with standard thickness materials, it should be very durable, and tearing should not be a concern if the extraction does not generate extreme shearing forces.

Read more: Tear Resistance in Flexible Circuits

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Category: Flexperts

Coupling buried vias with microvias can solve many manufacturing challenges.

When it comes to designs, we all make choices – material selections, feature sizes, via structures, components and more. Often, we also make tradeoffs.

Maybe the 0.8mm BGA you want allows standard vias, but the 0.5mm BGA takes up less space. Or you need impedance-controlled signals (which seems to be a requirement on almost all new designs), and line widths must be balanced with dielectric thickness and Dk values.

As packaging challenges mount, so does part thickness and layer count. For many designs, two of the biggest cost and risk drivers are aspect ratio and annular ring. These two attributes are often at odds with each other. There are ways to help them coexist.

Aspect ratio, or board thickness to drilled hole diameter, can be a limiting factor for a few different reasons. Keep in mind that there are two aspect ratios to consider. The first and most commonly thought of is the mechanically drilled through-hole. The second is the blind microvia.

Read more: Aspect Ratio and Annular Ring

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