One of the primary advantages of using a flexible circuit versus a rigid PCB board or wire as well as cord is the savings in weight as well as area. Flexible printed circuit board products are thin, extremely lightweight, as well as permit you to package in 3D, bending and folding to make necessary links, enabling you to shrink the overall bundle dimension or fit extra electronic devices in a similarly-sized device. As an example, a really regular two-layer construction for a versatile circuit is.010″, including coverlay as well as can usually be also thinner than that. Yet what occurs when you have a larger, larger part that is going to be constructed to this flexible circuit? Connectors can often surpass the adaptable materials and also call for special focus during assembly and also installment.
Let me share a tale. A two-layer FPC design required a big, heavy port in the facility of the flex as well as an FR4 support was consisted of for included assistance in that location, which is the advised design technique. As it was being set up, the designer observed split traces and also failings around. This was initially attributed to the FR4 not being thick enough to sustain the component. Due to the fact that time was tight (isn’t it always?), a second FR4 stiffener was included in the opposite of the flex as a short term fix to offer extra support before setting up the through-hole adapter. This adjustment did not totally resolve the concern, yet it did boost return enough to be able to satisfy the prototype construct.
As this relocated from model to pre-production quantities, the complete design was evaluated for yield renovation possibilities. A few different points were done mechanically: the density of the FR4 stiffener was boosted, and also the density of the adaptable products was also enhanced to offer extra support. What was most intriguing, is that it was likewise determined that because element location, finest layout practices were not complied with. The pads were not tear-dropped. The junction of the trace and pad area is just one of the highest possible anxiety locations of a flex layout and also it is always recommended to include the biggest fillets feasible to your flex designs. In this case, not just was the element placing tension on the pad to trace transition locations, those areas were already at high risk.
What are a few of things to consider to efficiently navigate the obstacle of a heavy part needed on a slim flex circuit? One of the first choices that requires to be made is whether to utilize an adaptable circuit with a stiffener or a rigid-flex building. There can be confusion with regard to the terms of a rigidized flex when compared to a rigid-flex. To be clear, a rigidized flex is an adaptable circuit with an FR4 stiffener added to give assistance to component areas. This support is purely mechanical support. A rigid-flex, on the other hand, will normally have circuitry on the inflexible layers as well as use layered through-holes to electrically link the rigid and flex layers.
This decision needs to factor in the full scope of the flex as well as setting up, not simply the bigger much heavier port location. Frequently, with reduced layer matter flexible circuits, a flex style with included FR4 support is a rational, reduced expense alternative to a rigid-flex. Yet a rigid-flex building and construction must not be readily rejected if there are several, greater density component locations, particularly on both sides of the board.
When the decision is made to move forward with a rigidized flex, there are numerous things to consider with the layout. Initially, what is the form as well as density of the stiffener? Generally, FR4 stiffeners are created by taking stiff board laminate as well as engraving the copper on both sides, then piercing as well as transmitting the proper shapes and size. Usual FR4 support densities range from.003″ (0.008 mm) to 0.125″ (3.18 mm). The general dimension of the stiffener ought to consist of a review of not only the dimension of the part being supported, however likewise exactly how that support could influence neighboring bend and also fold locations.
As soon as the support is created, a choice needs to be made as to just how the support will certainly be bonded to the flex circuit. Will bonding the support to the flex with a pressure-sensitive sticky suffice or will the application require a thermal collection adhesive to made use of? PSA’s are commonly a lower-cost choice, not needing an extra lamination cycle by the fabricator.
We talk quite a bit regarding following good style methods for versatile circuit layouts including tear going down the pads, supplying tie downs or rabbit ears for those pads, transmitting vertical to any bend as well as fold locations, maintaining plated through-holes away from flexing and folding areas, etc. As we saw from the instance earlier, this is important even if the location is most likely to be supported by a stiff support. Bypassing these suggestions can prove to be a pricey faster way.
One last recommendation when using a rigid support to support a heavy part on an adaptable material is to be sure to add an entry in the construction notes to have epoxy applied at the flex as well as stiff user interface to help reduce the stress on the traces in that location.
Don’t be nervous concerning utilizing a larger, much heavier element on a thin, lightweight flex circuit, simply be sure to follow the best techniques for design!
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