If you are looking for small volume electronic products that must be highly reliable while operating at high frequencies and high insulation in environments with high pressure, high temperature, and high pressure, Metal Core PCBs (MCPCBs) may be a good choice. However, there is other alternative — a ceramic PCB.

Characteristics

A brief overview of the basic structure of ceramic PCBs offers an insight into why they offer such excellent performance. Usually, ceramic PCBs are made from 96-98% Alumina (Al2O3), Aluminum Nitride (AIN), or Beryllium Oxide (BeO). Although for thin or thick film technology, silver palladium (AgPd) is preferred as the conductor material. For the requirement of direct copper bonding, copper is used. Ceramic PCBs can operate in the temperature range of -55°C to +850°C, and they have excellent thermal conductivity ranging from 24-250 W/m-K, depending on whether the ceramic material is Alumina, Aluminum Nitride, or Beryllium Oxide. Ceramic materials exhibit great compression strengths of above 7000 N/cm2, with breakdown voltages of up to 28 KV/mm for 1.0mm thickness. The thermal expansion coefficient under operating temperatures of 50-200°C is about 7.4 ppm/K.

Types of Ceramic PCBs

Depending on the manufacturing method, three basic types of ceramic boards are available in the market:

• Thick Film Ceramic Boards
• Thin Film Ceramic Boards
• DCB Ceramic Boards

Thick Film Ceramic Boards

These are so called because of the thickness of their conductor layer, which may exceed 10 microns, but not more than 13 microns. The conductor layer is usually silver or gold palladium, and printed on the ceramic substrate.

The advantage of thick films on ceramic boards is manufacturers can put interchangeable conductors, semi-conductors, conductors, electric capacitors, or resistors on the ceramic board. After completing the steps of printing and high-temperature sintering, all the components on the board can be laser-trimmed to their desired values.

Thin Film Ceramic Boards

The thickness of the conductor layer in thin film ceramic boards is less than 10 microns and deposited on the ceramic substrate using thin film manufacturing technologies such as electroplating, sputtering, or evaporation. The thin films are useful in producing on-board passive networks, assemblies for micro-components, and hybrid integration of circuits formed by packaging.

Depending on the concentration of component parameters and the distribution of the passive networks, thin film ceramic PCBs may be further categorized into lumped or distributed parameters. While lumped parameters cater to frequencies lower than that used for microwaves, the distributed parameters are meant for operating within the microwave band alone. Usually, the equipment used for manufacturing thin film ceramic boards is more expensive than those used for making thick film types. In addition, the cost of production is higher for thin film technology.

Thin film ceramic PCBs are very useful for analog circuits such as for microwave circuits, as they need to exhibit high accuracy, greater stability, and excellent performance.

DCB Ceramic Boards

Direct copper bonded (DCB) technology represents a special process where a copper foil is bonded on to the ceramic core (AIN or AL2O3) on one or both sides. The bonding takes place under high temperature and pressure.

This type of bonding not only gives the super-thin DCB substrate high bonding strength, but it also has excellent isolation, high thermal conductivity, and fine solderability. Showing high current loading capacity, the DCB ceramic board can be etched similar to normal FR4 PCBs are.

Conclusion

At PCB Global, we have the capability not to only provide ceramic PCB’s, but to also assist you with any design specifications or inquiries you may have regarding the general use and outcome of the purpose of your ceramic board and also determining if a ceramic PCB is the right choice for your requirements. For any questions or if you would like to arrange a quote for your ceramic PCB, please don’t hesitate to contact us as sales@pcbglobal.com

PTFE or polytetraflouroethylene, commercial name Teflon, has an inert molecular structure that makes it an excellent material for use as non-stick coating. PCB fabricators are increasingly using PTFE laminates compared to conventional FR4 materials, because of the unique properties of PTFE that allow it to be used for high frequency applications. Although fabricating PCBs made of PTFE is very similar to those followed for conventional PCBs, fabricators need to be careful in handling the rather soft material, and fine-tune their processes with special emphasis on those areas where PTFE differs from traditional materials because of its unique properties and chemistry.

For instance, PTFE laminates are soft and the surface is able to bend, wrinkle, or dent more readily than their FR4 counterparts. While such surface imperfections are acceptable in consumer electronic circuits, they can significantly affect functional performance in high frequencies. Therefore, PTFE laminates need a flat support while storing, to prevent them from sagging or drooping, as this can set over time.

Surface Preparation for Metallization, Marking, and Multilayering

It is not advisable to prepare the copper surface of a PTFE laminatemechanically. Equipment such as bristles, pumice scrubbers and composite brushes suitable for conventional rigid material should not be used as the soft PTFE substrate could stretch to absorb the stresses leading to unpredictable dimensional results.

To prepare the PTFE surface, the standard process that the PCB industry uses is Sodium Etchants or Plasma Gas Cycling. These processes strips or removes the fluorine from the PTFE surface making it suitable for metallization, marking, and multilayering.

To avoid problems associated with registration resulting from dimensional stretching, fabricators use soap or a degreasing bath to remove the potential organics. They also use chemical cleaning to remove anti-tarnish coating on the copper foil. This typically removes about 40 millionths of an inch from the surface of the foil to promote photoresist adhesion.

Lamination

PTFE and copper films can bond without the use of bonding films and/or prepregs. Usually, fabricators use temperatures of 700F and pressure of 450-500 psi as a starting point for the lamination process. The temperature and pressure changes with ceramic filling and other compositions of the PTFE laminate.

Fabricators also use bonding films with lower melting point for reducing the processing temperatures to about 250-425F. Others may use ceramic filled bonding plies as woven glass reinforced prepreg, requiring process temperatures of 550F.

Drilling

Although there are no hard and fast rules while drilling copper laminated PTFE substrates, it is essential to employ new tools at all times. Typically, slow infeed and higher chiploads are preferred for eliminating spurious laminate fibers or PTFE tailing.

Fabricators achieve additional benefits such as easier drilling and cleaner holes with ceramic-filled laminates, as this material has a modified dielectric constant, and lower CTE. However, ceramics filling increases drill wear by 25-50%.

Metallization and Copper Plating

As pure PTFE laminates have a very high Z-axis CTE, it is necessary to use high tensile plated copper on the walls of through holes. Copper of high ductility reduces the chances of pad lift, barrel cracks, and blistering, as PTFE has an inherently low modulus.

Soldermask

Fabricators use a standard PTFE plasma cycle process prior to application of soldermask to enhance the SMOBC adhesion to the copper. For best results, application of soldermask should preferably be completed within 12 hours of circuit etching.

Conclusion

At PCB Global, we currently fabricate Teflon PCB’s for microwave applications and the defence industry and have the knowledge, experience and capability to advise our customers on the use of Teflon base material PCB’s and how this can be implemented for their custom PCB design for their intended application. For more information or any inquiries of Teflon PCB’s, please proceed to contact us or simply email your Teflon base design file for a fast quotation to sales@pcbglobal.com

Introduction

Although Light Emitting Diodes (LEDs) operate at very high efficiencies, they do produce heat as a byproduct and this has to be removed if the LED is to operate continuously. As the heat generation in a semi-conductor, such as an LED, happens in the PN junction, the only way to remove it is via one of its leads. Manufacturers prepare special Printed Circuit Boards (PCB’s), which help in removing this heat by conducting it away from the lead and junction of the LED mounted on the PCB. IN this case, PCB’s are manufactured using a base of aluminum, and their names vary from aluminum PCB’s, insulated metal substrate (IMS), aluminum clad, metal clad (MCPCB), and thermally conductive PCB’s.

Mostly used as single-sided, aluminum based copper clad PCB’s have a copper foil bonded onto a thin thermally conductive but electrically insulating dielectric, which in turn is bonded onto a thick aluminum base. The copper layer is processed in the regular way to form the traces, while the profile is machined to the necessary size and shape. During the manufacturing process, the aluminum substrate needs protection from the etching chemicals.

Although this arrangement is specifically suited for population with surface mount devices (SMDs), through hole components are also used, in which case, the PCB’s are usually double-sided or hybrid types. Apart from LEDs and power converters, automotive and RF companies also take advantage of the thermally conducting properties of aluminum PCB’s in their applications.

Benefits of Aluminum PCB’s

• Dramatic increase in heat dissipation, as compared to conventional PCB’s using FR-4 material.
• The base of laminate is mechanically rigid.
• High reliability and MTBF, as thermal stresses on components are low.
• Improved heat transfer allows thinner tracks of lower width for high current designs.
• Smaller PCB’s on account of better thermal management, leading to higher component densities.
• Relatively lower cost compared to FR-4 PCB with heat sinks.

Types of Aluminum PCB’s

The single-sided aluminum based copper clad PCB is the most commonly used. However, other configurations are also available. Therefore, one can have hybrid aluminum PCB’s, flexible aluminum PCB’s, multilayer aluminum PCB’s, and Aluminum PCB’s for through-hole components.

Hybrid Aluminum PCB’s

These are usually conventional FR-4 or PTFE grade PCB’s of 2 or 4 layer construction, bonded on to an aluminum base with thermal materials. This assembly improves heat dissipation and rigidity, while acting as a shield.

Flexible Aluminum PCB’s

These are relatively new developments using IMS with flexible dielectrics. The dielectric material is mostly a polyimide resin system with ceramic fillers to improve the electrical insulation, flexibility, and thermal conductivity. This is applied to a flexible aluminum material that allows forming to different shapes and angles. However, this arrangement does not flex regularly.

Multilayer Aluminum PCB’s

High performance power supply designs commonly use this type of PCB’s. They are made of multiple layers of thermally conductive dielectrics combining layers of circuitry within them. Blind vias carry heat to the aluminum layer for dissipation, although the efficiency of heat transfer is not as good as that of single-layer boards.

Through-Hole Aluminum PCB’s

The Aluminum layer forms the core of the multilayer thermal construction. The aluminum layer is pre-drilled and back filled with dielectric. This is done before laminating it with thermal bonding materials on both sides. The completed assembly is then drilled through and plated. Clearances in the aluminum layer maintain electrical insulation.

Conclusion

At PCB Global, we commonly produce aluminum PCB’s and have the knowledge, experience and capability to advise our customers on the use of aluminum PCB’s and how this can be implemented in their specific design, for their intended application. For more information or any inquiries of aluminum PCB’s outside of our online capabilities, please proceed to contact us at sales@pcbglobal.com

Introduction

While designing multi-layer Printed Circuit Boards (PCB’s), one of the most basic elements that the engineer must include is the requirement for interconnected traces/planes on one layer to traces/planes on another. The most efficient technique of achieving this is to use vias. These are small holes drilled into the layers of the PCB, and fitted with a copper tube connecting to pads on either end. The pads in turn connect to the required traces on respective layers.

Why use Vias?

With increasing use of high-density boards, and engineers must reduce trace widths and spacing to accommodate for applications. Vias are another technique of achieving higher density boards by making them in multiple layers. In turn, the design of vias has also been evolving, with designers and engineers trying out different types of vias such as ‘landless’ and ‘swing types’. One of the very effective methods of achieving increased layer density is by using ‘via-in-pad’ designs.

Example

Consider the plight of an engineer in the process of breaking out the connections from an FPGA or BGA package of, for example, 1760 pins with a 1mm pin-pitch. According to the application data sheet of such a package, 6 signal layers are necessary to breakout the connections from all the pins. However, with advanced via techniques, engineers can now accomplish this with only 2 signal layers, resulting in better interconnection as well as being a substantial cost saving option.

Fabricators using the high-density interconnect (HDI) techniques use advanced technology such as buried vias, blind vias, via-in-pad, and micro-via techniques to improve the density of their boards spectacularly. Micro-via techniques involve using lasers to drill holes of very small diameter. Together with the via technologies above, the use of micro-vias results in 24% increased routing density per layer over conventional design processes.

How do they work?

As the name suggests, via-in-pad is a via deliberately placed within the area of a solderable pad. Normally, conventional design practices prevent the use of a via very close to or within a solder pad. Most manufacturers also recommend not using a via this way. The main reason being the via often acts as a wick does during the reflow process, allowing all the solder paste to melt and flow into its hole, leaving the solder pad starved of solder and resulting in an unsoldered joint. This problem is solved by filling and capping the hole of the via-in-pad.

Therefore, just as with any other tool, via-in-pad technology can lead to spectacular results if used properly, or to disastrous consequences if misused. For instance, inadvertently leaving a via-in-pad uncapped under a BGA solder ball can result in the solder paste flowing down into the hole of the micro-via, leaving the joint open. Therefore, it is essential to have every via-in-pad filled and plated over. To be on the safe side, all vias on the board are filled and plated over, and this effectively takes the via out of consideration.

While filling and capping the via-in-hole does solve a major problem, it creates another one—lack of coplanarity. Unless care has been taken to achieve good planarity, there can be a tiny bump or an indent over the via. This can lead to a less reliable assembly, especially with chip scale and BGA packages.

Conclusion

To discuss whether integrating the use of via-in-pad technologies for your PCB specifications, please feel free to contact the team at PCB Global for the most efficient advice followed by a rapid quote.  Please email you design file to sales@pcbglobal.comfor a rapid and competitive quote. 

Introduction

Manufacturing a multi-layer flex circuit board starts with a base material of copper clad flexible laminate. This is typically an unreinforced film coated with adhesive on both sides, with the outside surfaces covered with a thin sheet of copper. A lamination process bonds these elements together under heat and pressure.

The Materials

Such copper clad flexible laminates come in large sheets such as 24x36 inches—one of the standard sizes. The laminate material must be of the correct size and thickness, and be free from imperfections in the copper surface, such as pits and dents. After certification of the size and quality, a shearing machine cuts the full-size sheets down to more usable panel sizes, such as and typically 18 x 24 inches. To remove moisture and balance any internal stresses evenly, the panels are baked in ovens and then cooled before use.

The Process

1.    Using the computer-generated drilling information provided, the computerized drilling machines will drill holes in the panel as per specification. At the same time, the machines drill two or more ‘locating’ or ‘registration’ holes on the periphery of the panel to enable lining up the different films for further processing.

2.    The panel now undergoes a preparation process for the application of the conductive pattern. Usually, the chemical process starts with the panel being dipped in an acid bath, followed by the application of an anti-tarnish agent, ‘micro-etching’, or ‘chemical cleaning’. The next step involves creating the conductive pattern on the copper surfaces of the panel according to the circuit image.

3.    Following these steps, the image is transferred using a dry film. This is achieved through thedry film laminator using heated rollers to press a layer of photoresist onto each copper surface.Next, a sheet of film containing the negative image of the desired conductor pattern is placed on this layer of photoresist, and the sandwich is exposed to UV light inside an exposure chamber. UV light passing through the clear areas of the image sets up a chemical reaction in that area of the photoresist layer it touches. The unexposed areas remain relatively soft and a developing process in the followingstep removes this soft and unexposed resist, exposing the unwanted copper.

4.    Next follows an etching process, where a chemical solution removes the unwanted exposed copper from the surface of the panel. The required copper circuitry remains on the panel underneath the photoresist. Another chemical strips the hardened photoresist to expose the remaining copper.

5.    After a thorough inspection of the copper pattern, a very thin film of electroless copper is chemically deposited over both the surfaces of the panel, including inside the holes, also called vias. The metalized vias now connect one side of the flexible circuit to the other. Subsequent copper layers are added to the core over a layer of insulation called prepreg, and bonded to it using heat and pressure.

6.    Depth-controlled drilling then creates the blind and buried vias, followed by the same process of image transfer, etching, and electroless copper deposition on all the added layers.

7.    Finally, all the areas that will not be coated with solder are masked off with a coverlay. The finished flexible circuit board then undergoes an inspection process.

Conclusion

For more information on this particular process or for any advice on if your PCB specification should incorporate a flexible circuit element, please don’t hesitate to contact the team at PCB Global.  Please email you design file to sales@pcbglobal.comfor a rapid and competitive quote.