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In the modern world, complexity of electronic products has increased due to the demand for higher performance such as faster data transfers, better image processing, higher computing power, and greater functionality. This has resulted in higher component count in PCBs, higher signal frequencies of the order of 5GHz and more, high-speed interfaces such as HDMI, DDR-3/4, Gigabit ethernet, and HDI (High Density Interconnect) PCB technologies having blind and buried microvias. In the future, the demand for even higher performance from computers, mobiles, and communication devices would require PCBs to be designed to cope with even higher speed of operation and higher component densities.
Most PCBs can be considered to be at risk of some type of signal integrity problem that is normally associated with high speed digital design. High speed PCB design and layout focuses on creating circuit board designs that are less susceptible to signal integrity, power integrity, and EMI/EMC problems. While no design is ever totally free of these problems, by following these high speed board design guidelines they can be reduced to the point where they are unnoticeable and do not create performance problems in the final product.
There are special considerations one needs to take when designing a high-speed PCB:
1. All high-speed interconnections need to be designed as transmission lines and not just as point to point interconnections to reduce signal distortion, crosstalk and electromagnetic radiation.
2. All causes of signal degradations need to be kept under control within acceptable limits.
3. Adequate PCB technology is to be chosen so as to meet the demands of component density, wiring density, communication protocols, and complex devices.
4. All causes of unacceptable levels of electromagnetic radiation need to be kept under control.
5. Adequate power integrity has to be maintained in spite of high-frequency noise on power and ground rails in high-speed circuits – ensuring adequate power supply voltages are maintained at all the electronic devices and components for them to function properly.
6. Adequate and special PCB routing schemes need to be adopted to meet the demands of component density, wiring density, communication protocols, and complex devices.
The first three of the above points are usually covered under the disciplines called Signal Integrity and PCB stackup design, the fourth point is covered under the discipline called EMI, the fifth is covered under Power Integrity, and the sixth under Special layout routing techniques.
We will now discuss these in requisite details in the following sections.
The factors that influence impedance are the PCB materials dielectric, the trace thickness, width and height from the ground plane.
The designer should make sure that the manufacturer has the ability to provide the right pattern size, position, and tolerance. The board might turn out to be useless if these parameters aren’t achieved.
The two types of commonly implemented impedance controls are:
Controlled dielectric thickness:
The designer provides the controlled dielectric stack-up to the manufacturer. Since impedance traces are not specified here, the manufacturing focus is completely upon building a board within +/- 10% tolerance of the specified dielectric thickness from layer to layer.
Here the impedance is controlled through the dielectric thickness, the trace width, and space. The manufacturer performs a test to ensure that the desired impedance can be achieved using TDR coupons. Some adjustments are made depending upon results from the first articles in order to meet the designer’s needs and the boards are manufactured within the specified tolerance.
High-speed designs demand critical signal integrity requirements and crafting a PCB with the right stack-up becomes part of the overall signal integrity equation. The selection of the PCB materials for impedance, dissipation, and other signal characteristics along with the right order and number of layers of the materials, need to be considered.
A stack-up, also known as build-up, is the construction of a multilayer PCB in a sequential order. Almost 99% of the time, the stack-ups will be symmetrical. The stack-ups are made up of cores, prepregs and copper foils. The majority of the products fall under 62-mil board thickness.
The PCB construction depends on the component packages used in the design, required signal trace density, and impedance matching requirements. For the high-speed PCBs, using a multilayer PCB with buried ground and power supply planes is mandatory. Solid copper planes allow designers to keep the device ground and power connections short. Further, the ground plane offers low inductance return paths for the high-speed signals.
An accurately stacked PCB substrate will effectively reduce electromagnetic emissions, crosstalk, and improve the signal integrity of the product. A poorly arranged stack-up might increase EMI emissions, crosstalk and also the device becomes more susceptible to external noise. These issues can cause faulty operation due to timing glitches and interference which dramatically reduces the performance of the product.
With the right stack-up, the designer can suppress the noise at the source rather than correcting the issues after the product is built. PCBs involving multiple planes enable signals to be routed in microstrip or stripline controlled impedance transmission line configurations. The signals are tightly coupled to the ground or power planes and improve signal integrity by reducing crosstalk.
In high-speed PCBs, the ground and power planes perform three significant functions:
• Controls crosstalk amongst signals
• Deliver stable reference voltages for exchanging digital signals
• Distribute power supply to all the logic devices
While choosing a multilayer stack-up the designer should consider the following:
• A signal layer should always be placed right next to a plane.
• The signal layers should be tightly coupled (<10 MIL) to their adjacent planes.
• A power plane or a ground plane can be incorporated for the return path of a signal.
• Determine the return path of the signals. The high-frequency signals take the path of least inductance.
The most common PCB material is FR4. This material is used in most electronic applications. However, when it comes to high-frequency signals, especially in the microwave domain, FR4 is not suitable.
When designing PCB circuits at microwave frequencies, the key characteristics that define circuit laminate performance for microwave/RF printed-circuit boards include:
• Dielectric constant(Dk)
• Dissipation factor (Df)
• Coefficient of thermal expansion (CTE)
• Thermal coefficient of dielectric constant (TCDk)
• Thermal conductivity
The high-frequency material perhaps most familiar to users of PCB laminates is polytetrafluoroethylene (PTFE) which is a synthetic thermoplastic fluoropolymer that has excellent dielectric properties at microwave frequencies. Rogers materials are also commonly used.
Signal integrity starts with designing to a specific impedance value in your board and maintaining that during layout and routing. Some other strategies to ensure signal integrity include:
These important points can be encoded as design rules for your routing tools, which will help ensure you comply with best practices on high speed design.
The design rules you set in your high speed design project will ensure you meet impedance, spacing, and length targets as you route your design. In addition, important rules in differential pair routing can be enforced in your routing, specifically minimized length mismatches to prevent skew and enforced spacing between traces to ensure differential impedance targets are met. The best routing tools will allow you to encode your trace geometry limits as design rules so you can ensure performance.
One of the most important points in high speed PCB routing is placement of ground planes near your traces. The layer stack should be constructed to have ground planes in layers adjacent to impedance controlled signals so that consistent impedance is maintained and that a clear return path is defined in the PCB layout. Traces should not be routed over gaps or splits in ground planes in order to avoid an impedance discontinuity that creates an EMI problem. Ground plane placement isn’t limited to ensuring signal integrity, it also plays a role in power integrity and ensuring stable power delivery.
Ensuring stable power delivery to high speed components is critical in PCB design as power integrity problems often masquerade as signal integrity problems. They also create unnecessary radiation from interconnects and buses as transients create strong oscillations that radiate strongly. To ensure stable power delivery, use decoupling capacitor groups with a range of self-resonances to ensure the design will have low impedance over the broadest possible bandwidth. Using a power and ground plane pair on adjacent layers provides additional capacitance to help keep PDN impedance low.
Another reason why high-temperature laminates are so important when working with PCBs is that potentially damaging heat can come from almost anywhere, with unpredictable effects. If you assume heat will not be a problem for your PCBs, you may be in for a rude awakening. If you’re not clear on exactly where your potentially damaging heat effects may be coming from, some possible heat sources include:
Rather than try to anticipate where heat sources will come from, if there is any chance you will be using your PCB in a high-temperature environment, you want to make sure you are using circuit materials designed to resist the effects of high temperature, including high-temperature laminates.
The most common high temperature polyimide materials include:
Hemeixin custom manufactured many double-sided, high-temperature printed circuit boards (PCBs) for a client from the Telecom/IT Industry. These PCBs are capable of withstanding continuous operating temperatures of 250° Celsius.
Some of the processes used to manufacture these boards included:
In addition to these processes, hot air solder leveling was also performed, adding an extra layer of protective metal over the copper surface. Holding tolerances as close as ±.005″, the finished PCBs were constructed from polyimide laminate and measured 10.5″x 3″. Meeting stringent industry standards and client specifications, we delivered all finished units to our consumer’s facility in Worldwide. The units fulfilled our customer’s high expectations for both quality and high temperature reliability.
High Density Interconnect PCB, with microvia≤0.15mm， use fine feature technology to connect components in small packages. HDI’s smaller geometry allows for higher wiring density. The electrical performance is greatly improved because of control on lower parasitic, minimal stubs, removal of decoupling capacitors and lower crosstalk. RFI and EMI is much lower due to ground planes being closer together, distributed capacitance is closer.
Many electronic applications are seeing a need for increasingly faster frequencies. As frequency increases, the margin for error and/or deviations in the pcb is significantly reduced. The use of high frequency material like PTFE substrates, blind vias and tightly controlled etch tolerances are required to achieve such high frequencies.
High layer count PCBs, widely found in file servers, data storage, GPS technology, satellite systems, weather analysis and medical equipment are usually ≥12L with special performance requirement raw material.
MCPCB, A metal-based PCB, is comprised of a metal substrate (ie Aluminum, Copper or Stainless Steel ect.,), thermal dissipating dielectric and the copper circuit. Due to its superior heat dissipation, MPCBs are used for a wide array of applications. You can find them in power supplies, LED lighting or anywhere that heat is a major factor.
The conventional PCBs have electrical connection on the normal FR-4 material through the vias. After a long-term development, it has evolved from single-layer to double-layer, multi-layer PCBs.
What information is required to fabricate a countersink holes pcb?
Countersinks most commonly will have either an 82 degree or 90 degree angle so a primary consideration is the desired angle. Additionally, you would need to specify the diameter of the smaller hole, and either the maximum diameter or the depth of the countersink. And, whether that hole is to be plated or non-plated. In most cases, these are non-plated but there could be situations where you may be grounding to a chassis and would need to have plating in the hole.
Why build selective gold plating pcb?
The hard gold finish basically offers tough resistance to friction compared to other finishes. It is used to create gold fingers on circuit boards. This finish is the best option when a PCB is designed to be inserted into another board, such as RAM. Hard gold is extremely durable, thus can withstand repeated usage. This finish is expensive and has poor solderability, hence, it is not applied on solderable surfaces.
For any areas on a circuit board that will require wire bonding or touch pads, ENIG is often a good choice. Organic solderability preservative (OSP) is good match for the ENIG finish, as it is lower in cost and will not harm the gold. The process of combining OSP and ENIG is referred to as “SENIG” or selective ENIG. The problem with using the ENIG and OSP process for manufacturing is the potential corrosion of the nickel used in the product. The nickel used must be highly resistant to corrosion, as the processing of the OSP finish leaves it vulnerable.
Whenever there is a requirement to plate specific areas on the board with hard gold, you can opt for selective gold plating. The process of selective gold plating is a bit different. For this reason, it is necessary to specify your requirements while raising a quotation.
Press-fit holes are plated through holes with tighter tolerances than the standard +/-0.10mm. Press-fit holes fit the leads of connectors that will not be soldered but pressed into the holes. To accommodate lead and hole to tightly fit together, the tolerances are well defined and more tight than standard.
The typical tolerances for the PTH depends on the type of connector, which is specified by the connector manufacturer.
Therefore it is of utmost importance that these tolerances are well defined in your PCB data and that the parameter “Press fit” is checked in the order details.
SEMI-FLEX is flex to install. Unlike polyamide, the FR4 core is not capable of continuous flexing.
With simple depth-milling a standard printed circuit board can be prepared for flexible installations. So called "semi-flexible" printed circuits are offering a cost-efficient solution. They save connectors and increase reliability while decreasing size of the application and time needed for assembly. Semi-flexible PCBs are the perfect solution if you have flex-to-install requirements only and there is no dynamic bending during operation.
Production of a semi-flexible PCB is identical with the manufacturing process of standard printed circuits. Semi-flexilbe boards can be produced as single-layer, double-layer or multilayer PCBs. With the exemption of a special solder mask that sustains bending, the materials are also identical to standard printed circuits. The only difference happens at the end of the production process when dedicated bending areas are milled down by z-axis routing. The remaining material can be bend and is thin enough to only carry the copper traces and little base material.
However it will bend a limited number of times at a controlled radius and to any angle.
This makes it an ideal solution where you need to mount two PCB’s in a unit at an angle to each other. Instead of using connectors and cables or a composite flex-rigid PCB, you can design a single FR4 SEMI-FLEX PCB which can be safely bent a sufficient number of times to allow installation and subsequent maintenance as needed.
Why hard gold pcb?
For the Hard Gold Plating, the entire panel is covered by tape. Only the part that requires the application of a surface finish is removed. Unlike ENIG, in this case, the copper thickness can vary by controlling the duration of the plating cycle. The nickel is first electrodeposited, then the gold is deposited according to the customer's request. The gold thickness provides an excellent shelf life but also one of the most expensive surfaces finishing options. To sum things up, Hard Gold Plating surface finish has mechanical properties, excellent shelf life and provides a flat surface. There are also drawbacks such as high cost, poor solderability and the process is complex.
Often a PCB is used in combination with a membrane switch where the underlying gold must withstand many actuation forces of a keypad. The gold plating on tabs of a keypad is usually defined by the engineer at 200-300 micro inches. Hard gold is meant to survive many actuation forces or insertion and removal up to 1,000 actuations or more.
To better understand the longevity, think of your keyboard or calculator. Each depression to make a contact must hold up to long usage. This type of gold plating is electroplated or electrolytic plated by using an electrical charge as opposed to a purely chemical reaction. Thickness may be controlled by varying the plating cycle time. Thickness is usually between .000015”-.000050” standard processing.
Flash electrolytic is a thin coating of hard gold. Unlike thicker hard gold coatings, flash gold remains solderable for SMT assembly because its coating thickness is approximately 10% as thick as hard tab gold. Like ENIG, its thickness range is limited – typically .0000015”-.000003” thick.
Hemeixinpcb offers two types of gold finish: Electroless Nickel Immersion Gold (ENIG) as a surface finish for the whole PCB, and hard plated gold over plated nickel for edge-connector fingers. Electroless gold gives excellent solderability, but the chemical deposition process means that it is too soft and too thin to withstand repeated abrasion. Electroplated gold is thicker and harder making it ideal for edge-connector contacts for PCBs which will be repeatedly plugged in and removed.
Hard gold finish, also known as electrolytic hard gold, is made of a layer of gold with hardeners that will maximize durability. Using an electrolytic process, it is plated over a nickel barrier coating. The thickness of this plating varies according to the duration of the plating cycle.
The plating procedure uses gold because gold has high corrosion resistance, high electrical conductivity, and can be alloyed with cobalt or nickel to develop resistance to wear and tear. Gold plating can range in thickness from 3µ” to 50µ”.
Why are castellated hole?
A popular trend among manufacturers is board-to-board soldering. This technique allows companies to produce integrated modules (often containing dozens of parts) on a single board that can be built into another assembly during production. One easy way to produce a PCB that is destined to be mounted to another PCB is to create castellated mounting holes. These are also known as "castellated vias" or "castellations."
Plated half-holes (or castellated holes) are predominantly used for board-on-board connections, mostly where two printed circuit boards with different technologies are combined. E.g. the combination of complex microcontroler modules with common, individually designed PCBs.
The board-on-board PCBs therefore need plated half-holes, which serve as SMD connection pads. Through directly connecting the PCBs together, the whole system is considerably thinner than a comparable connection with multi-pin connectors.
Hemeixinpcb is your one-stop shop for all types of PCBs – Printed Circuit Board Manufacture, PCB Design, PCB Fabrication Full Turnkey PCB Assemblies . We specialize in high layer count PCBs, Engineering Prototypes, and the full range of Electronics Manufacturing Services. Every PCB is built to the highest quality standards, including Rigid PCB, Flex PCB and Rigid-Flex PCB. All PCB assemblies are built and certify accordingly ISO 9001:2015, ISO 14001:2015, ISO/TS 16949:2016,J-STD-001, IPC-A-610E .PCB, PCB Design, Fabrication, Our Electronic Assembly Service is unmatch anywhere in speed, quality, and workmanship. From bare circuit boards to box build and final assembly, Hemeixin Electronics Co.,Ltd. is your premier one-stop shop, with the most competitive pricing in the industry and a commitment to total customer satisfaction.