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2019年05月

A Printed Circuit Board Is Not Always a “Board”

When the term “PCB” is used, many people think of a rigid PCB (printed circuit board). However, the term PCB can refer to either a rigid PCB or a flexible PCB. Flexible PCBs are more commonly known as flex circuits, but they are also known by other names including flex boards, flexible circuit boards, flexible printed circuit boards and, more officially, flexible electronics. Flex circuits have recently gained huge popularity due to the fact that they can be shaped, bent, twisted, and folded into limitless configurations. In the end, however, rigid PCBs and flexible PCBs serve, in the most basic sense, the same ultimate function, which is connecting various electrical and mechanical components together.

When to Use Rigid and When to Use Flexible

Rigid PCBs typically cost less than flex circuits. I say “typically” because when considering the total cost of ownership there are some applications that, when using flexible PCBs, may be less expensive compared to using rigid PCBs. To get a true and accurate understanding of the total cost of ownership, you first need to appreciate the fact that flex circuits may eliminate the need for components such as connectors, wire harnesses, and other circuit boards. By removing these components from a design, material cost, labor and assembly cost, and scrap cost are all reduced.

Many electronic devices (laptop and desktop computers, audio keyboards, solid-state drives (SSDs), flat-screen TVs and monitors, children’s toys, and various electronic gadgets) employ rigid PCBs instead of flexible PCBs. However, flex circuits may be found in ultra-compact and/or high-performance devices, including GPS units, tablets, smart phones, cameras, and wearables.

Greater sophistication is not the only reason to use flex circuits; low-tech applications (such as under-the-counter LED lights, see figure below) may utilize flex circuit technology, in some cases because it makes installation much easier.

Finally, a flex circuit and a rigid circuit can be used together—as a unified PCB—if the need arises. This approach, perhaps, provides the best of both worlds. See Figure 2 below.

Some Similarities and Differences Between Rigid PCBs and Flex Circuits

When designing rigid PCBs, certain design rules must be followed, including minimum hole sizes, minimum space and trace width, minimum distances to board edges, and copper and overall design thicknesses. Additionally, many manufacturing process steps are shared between rigid and flexible PCBs. Such process steps include the drilling and plating of holes and vias, photo imaging and development, the etching of copper traces, pads, outlines, and planes, and the heating (baking) of the circuit boards for the purpose of removing moisture from the PCBs. At this point in the manufacturing process, rigid PCBs head to the solder mask station while flex circuits go to the coverlay station.

Flex Circuit Overlay

Flex circuit overlay, or coverlay, as it’s also known, is a lamination process used for encapsulating and protecting the external circuitry of a flex circuit. A flex circuit’s coverlay film is similar to a rigid PCB’s solder mask, with one big difference…the coverlay film is flexible! According to allflexinc.com, “The coverlay film is generally a polyimide film that is coated with a thermoset adhesive. Film thicknesses range from .0005” to .005” with .001” and .002” the most common.”

The polyimide and adhesive coverlay is laminated using pressure and heat, where the heat helps the adhesive to easily flow and fill in any gaps between traces and pads; this prevents the trapping of air between the layers. Again from www.pcbjhy.com: “The adhesive flowing is necessary as it helps assure complete surface contact and encapsulation. The adhesive will tend to ooze out slightly around the openings shown in the diagram below. This oozing is commonly referred to as ‘adhesive squeeze out’ and is actually a desired phenomenon.”

Once the coverlay lamination process is finished, any component and/or feature openings are made using drilling, routing, or laser cutting. Etching cannot be used.


IPC Standards for Rigid and Flexible PCBs

The list of IPC standards below applies to rigid PCBs and flex circuits. Take note that this list is not exhaustive, and additional IPC standards may need to be considered. You should consult the ipc.org website for a full list of available IPC standards.

IPC-2221A, Generic Standard on Printed Board Design

IPC-2223, Sectional Design Standard for Flexible Printed Boards
IPC-4101, Specification for Base Materials for Rigid and Multilayer Printed Boards
IPC-4202, Flexible Base Dielectrics for Use in Flexible Printed Circuitry
IPC-4203, Adhesive Coated Dielectric Films for Use as Cover Sheets for Flexible Printed Circuitry and Flexible Adhesive Bonding Films
IPC-4204, Flexible Metal-Clad Dielectrics for Use in Fabrication of Flexible Printed Circuitry
IPC-6013, Qualification and Performance Specification for Flexible Printed Wiring


In Conclusion

Although both rigid and flexible printed circuit boards fundamentally serve the same purpose—connecting various electrical and mechanical components together—both technologies have their place in life. While many of the same design rules are used with both rigid and flexible PCBs, flexible PCBs require some additional rules due to their additional manufacturing process steps. And even though rigid PCBs may seem, at least initially, to cost less, one should definitely consider a design’s total cost of ownership before declaring that flex circuits are too expensive.

What is Gold Fingers PCB

As printed before, the term "Gold-finger PCB” is employed to consult with gold-plated connectors mounted at the interconnecting edges of a fringe PCB. different names to decision a Gold finger PCB abe re a Gold connection, Edge connection, Edge-Board connection, connection Finger, Contact Fingers, Gold faucets or Gold Tips.

It is potential you too might need interacted with Gold Fingers PCBs within the past. Wait, are you able to keep in mind interacting with a group of shiny wanting, finger-like projections on the sides of a change of integrity finish of a peripheral circuit board? Aha! that is what i'm talking concerning here. They agree fingers within the sense that they appear skinny and elongated at the contact edges of a PCB. Gold Fingers square measure typically fitted onto the sides of fringe PCBs or epitome boards to boost property with larger boards.

The edge connectors (i.e., gold fingers) also are plaited with flash gold (hard gold) with a thickness that varies between 3u’ and 50u’ (units in small Inches).

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Why Gold Plaiting is critical For Gold Fingers PCB

Primarily, PCB affiliation points square measure subject to constant plugging and unplugging due to their nature of interconnecting PCBs. Hence, while not a robust contact edge, they're at risk of wear-and-tear which will cause device out of whack. The act of plaiting the connectors with different metals (in this case gold) is finished to boost the sturdiness of the sting connectors. 

But i'm certain you may have wondered: of all metals, why ought to edge connectors be gold-plated? Isn’t gold too expensive? Couldn’t copper conduct higher and be a great deal cheaper than Gold? Well, I actually have associate degree answer: certain, gold plating of gold fingers is pricey, however it's necessary.

Gold was chosen over different metals as a result of to this point, gold has verified to possess high corrosion resistance, high electrical conduction (second to copper and silver) and will be alloyed with metallic element or nickel to extend its resistance to wear-and-tear. Earlier experiments that were done to determine the resistance of gold vis-à-vis its resistance and compared to different standard metals showed that gold had a lower resistance than different metals as shown in Table one below. 

Gold is additionally inert. It doesn't oxidize or react without delay with different metals. This property of gold builds it a perfect option to make the components that square measure at risk of be exposed or doubtless to react with different metals. although silver is typically helpful, it's not counseled for business productions as silver is vulnerable to chemical compound and chloride attacks.

Fast Prototyping & Manufacturing of Smaller, Lighter, and More Reliable Flex Circuits

Our technical teams can produce your standard flex prototype in 5 days and developmental flex prototype in 15 days. Challenge us with multilayer, sub 2-mil thickness, tight registration, and a high number of traces. Give us your toughest HDI with a specific RF performance requirement. Ask us to make your flex circuits smaller, lighter, and more reliable.

Our flex circuit capabilities can meet rigorous requirements, like these:

  • 1 mil (25 μm) trace/space
  • 25 μm vias and critical dimensions of laser ablated features to 10 μm
  • Complex 3+ layer HDI flex circuits that other shops won't touch

Why flex circuits?

Thickness & Package Size

Because flexible circuits use the thinnest dielectric substrates available for making electronic interconnections, it’s possible to produce flex circuits with a total thickness approaching 1 mil (25 μm), including a protective cover layer. A thin profile allows tighter spacing, thin traces, and in many cases, layer reduction.

Weight

Smaller circuits are naturally lighter. Some applications result in a weight reduction of 50% or more over rigid or rigid-flex designs. Our dielectric material sets are thin in dimensional thickness and use lighter “copper weights,” resulting in a lightweight, highly flexible circuit construction.

Reduction in Assembly Time, Errors, and Cost

Flex circuits can reduce product assembly time because they seamlessly integrate form, fit, and function into a single circuit. A reduction in assembly time also reduces manufacturing errors and costs.

Understanding Flex Circuits

Flex circuits are used in cars, computers and peripherals, digital cameras, and exercise machines. They’re found in industrial lasers, inductor coils, and heater coils. Medical uses include everything from hearing aids to ultrasound equipment to defibrillators. You’ll find flex circuits in NMR analyzers, x-ray machines, particle counters, and infrared analyzers. Flex circuits reduce production costs and enable devices like smartphones, instrument panels, plasma displays, and smart weapons to be lighter, highly flexible, and smaller, with fewer in-field reliability issues.


A single layer flex circuit features a single conductive circuit layer with top or bottom access to the conductors. Stiffeners and connectors are optional.


A double layer flex circuit has two conductive layers with insulating dielectric in between. Plated through-holes (vias) provide connectivity between layers, and there’s top or bottom access to the conductors. Stiffeners and connectors are optional. Read more about our laser micromachining and drilling capabilities that can create blind vias down to 1 mil.


A multilayer flex circuit has three or more conductive layers with insulating dielectric in between. It features blind or buried vias and top or bottom access to conductors. (A blind via extends to one surface only of a flex circuit; a buried via does not extend to either surface.)

We specialize in microvias—vias created with precision laser drilling techniques and that require dimensional and positional accuracy, which most firms cannot attain.

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