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  • Thermal Vias are Ineffective. Here’s Why.

    Thermal Vias are Ineffective. Here’s Why.

    Adding thermal vias can take up valuable board space with little benefit.
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  • Connecting the Industry, from Boards to Assemblies

    Connecting the Industry, from Boards to Assemblies

    HDP is embarking on new rounds of evaluations of laminates and lead-free solders.
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    Exploring the Impact of AI

    A special panel discusses the growth of AI tools and its possible effects on the industry.
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  • A Journey in Rigid-Flex Design

    A Journey in Rigid-Flex Design

    Overcoming the challenges of rigid-flex designs can be incredibly rewarding.
      READ MORE...

  • Creating the Ultra Library

    Creating the Ultra Library

    Building and maintaining what's said to be the world's largest CAD database requires strong relationships.
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Flexperts

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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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Category: Flexperts

White mask is possible, but careful of overexposure.

I am designing a flex circuit that will have LEDs in one area. I would like that area to be white in color instead of amber. What is the best way to do that?

Answer: A flex circuit can have a white outer surface, and this can be achieved in several ways. I will cover the different methods with the pros and cons for each.

Screen printing. For a "quick and dirty" solution, simply have that area of the circuit screen-printed with white ink (over the top of the standard amber polyimide covers). The downside to this method is that if you also want screened legend, a separate process using a contrasting ink color is necessary. Any LEDs must have clearance to ensure no ink ends up on the solder pads. This method will produce a white surface, but there may be rough edges and color tone variations. I would not recommend attempting any tight bend radius forming in areas with screen-printed ink. Some inks can crack if bent sharply, and if a crack forms in the ink it can, and probably will, propagate through the underlying polyimide film over time. And even if the cracks do not propagate through the polyimide film, the ink around the cracks will flake off and end up as FOD (foreign object debris) in the system.

Read more: Flex Circuits, in Color

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Category: Flexperts

Should you add a strain relief bead to your rigid-flex circuit?

You are putting the finishing touches on your new design and feeling pretty good – you have made both the mechanical and electrical teams happy. At least mostly happy. One nagging issue remains: Should you add a strain relief fillet or bead to the interface between the rigid and flex portions of your circuit?

IPC-2223 discusses strain relief and considerations for and against. An estimate may be that about 50% of all designs include stain relief, and the rest do not. Keep in mind that the guidance below applies to both rigid flex and also to flex with FR4 or metal stiffeners. How do you decide if yours needs it?

First, let's discuss the role of the strain relief bead. At its core, the goal is to avoid a very sharp bend of the flex right at the rigid/flex interface. Some are concerned resin may flow out from the rigid material that could create a sharp edge, and the flex may be bent sharp enough to be damaged by the sharp rigid or resin edge.

Read more: Relieving the Strain

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