Endless-snake flexible printed circuits

Endless-snake flexible printed circuits

Using a smart „snake“-layout trick and pre-applied 3M double side-adhesive, one can design easy to assemble, meter-long flexible pritned circuits. LED-stripes or extremely long connectors can be realised cheaply without questioning producibility or deviating from normal production standards. The FPC shown in this example reached a length of 4,50 meter. Longer flexible circuits with this "endless-snake" approach are perfectly possible.

Endless Snake Flexible Printed CircuitFor LED- or connectivity-technologies there is often the need for flexible printed circuits. But length of the FPC is limited by several constraints, mainly coming from the machines in production such as lamination press, drill machine, exposure machine etc. Additionally, very long flexible circuits are extremely difficult to handle during assembly process. Best-practice is to simply produce shorter flexible circuit stripes of around 500mm and use connectors to combine them to one long FPC. In other cases, these shorter stripes are connected by soldering them together. Both ways increase costs of assembly and the risk of functional failure while there is no saving made with the FPCs compared to the snake-approach. 

Endless Snake Flexible Printed CircuitThis innovative, fast and cost-saving idea with endless-snake FPCs may even be cheaper in actual production. The production panel can be utilized perfectly by adjusting the turns according to the desired length. Surcharges for extremely difficult to handle 500mm over-length FPC are not necessary. LeitOn can help you designing the snake-flex so that the optimum utilization is reached and costs can be kept at a minimum.

Endless Snake Flexible Printed CircuitWe recommend attaching 3M double-side adhesive on both ends of the FPC. The 3M protective foil is easy to remove and the FPC can be fixed onto it after bending conveniently. Without any connectors or soldering joints this standard flexible printed circuit can reach many meters of length just by a layout trick. Thin LED-stripes can be brought to 10 meters length easily. It is cheap, reliable, easy to install and simply a smarter way of solving this ongoing length-challenge. 

There are some design rules to follow when preparing your endless-snake FPC:

1. The end of the snake where the actual bending/folding is done need to be in one line. This simplifies the 3M attachment and reduces production costs of the FPC. 

2. As shown below, rounded inner corners with some distance for the folding to happen are desirable. We recommend around 2mm distance to assure a safe 180°-bend. Using this 2mm bending-distance allows the FPC to be bent gently and lowers the risk of tearing it or breaking the circuit due to a sharp fold. 

3. The thickness of the folded part depends on the FPC stackup and design and ranges between 0,4mm and 0,7mm. It can easily be accommodated in slots, cable ducts or being covered with transparent protective paint.

4. A tempting design maximization is the use of „0mm-slots“. We do advise against using 0mm-slots (0mm distance between the flex-snakes) because it increases the risks in several areas. A 0mm distance comes with the necessity to fold the FPC sharply in the bending areas which may lead to breaking the copper structures. Furthermore, the sharp ends of these slots are a design weakness with an immense risk of tearing.

In case you necessarily require 0mm-slots due to length constraints you have to make sure the final FPC is installed solidly later as these sharp ends may lead to tearing over time when even the slightest movements persist. You also have top very careful during the folding process. We will be able to produce such 0mm-slots if you add non-plated holes at the end of the slots (?2mm recommended). Additional copper annular rings (if space allows it) are increasing stability, too. The risk of tearing can be lowered by this approach.

The FPC is producible in this way but comes with significantly higher risks during assembly, installation and in the field.

CharacteristicValeu, description
FPC thickness 25µm to 100µm
double sided adhesive 3M467, ca. 50µm
maximum length depending on layout 10 to 12 meters, possibly longer
copper thickness 18 to 35µm, for 2-layer FPC standard 28µm
solder stop cover lay 25µm or 50µm with epoxy adhesive. Flex solder mask not recommended!
FPC material Polyimid adhesiveless oder adhesive-based (epoxy)
surface finish immersion nickel-gold (ENIG) or immersion tin
prints silk print or covering colour prints (onto cover lay, purely for visual purpose) 
cutting laser for prototypes, punching tools for FPC mass production

Your advantages of endless-snake FPCs compared to the common approach of connecting many short stripes are the following:

  1. Your FPCs are more fail-proof, as weak spots such as solder joints are avoided.
  2. Your FPCs are cheaper, because it is a standard product that induces its additional values solely by a layout trick.
  3. Your FPCs are easier to install, because folding and sticking it onto 3M are fast and simple steps.

Your direct way:
+49 (0)30 701 73 49 0


LeitOn Leiterplattenproduktion Berlin

LeitOn GmbH, Wolframstraße 96, 12105 Berlin - Deutschland
+49 (0)30 701 73 49 0
Registered Court:
HRB 94175 B, Amtsgericht Charlottenburg

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