High power DC DC converter Aluminum mcpcb aplication

High power DC DC converter Aluminum mcpcb aplication
The MCPCB commonly consists of a metal core layer (typically aluminum or copper), a continuous dielectric layer and a copper circuit layer. Protecting electronic components by removing heat, metal base boards feature a thermally conductive dielectric layer connecting IC’s to the heatsink.
Sample Metal Boards

Industries
LED Lighting (general, automotive, and backlighting) to include high-current and spotlight, Electric Vehicles, Alternative Energy to include Solar applications, High Density Power Conversion, Motor Control, DC-DC Converters and Flat Panel Displays. Automotive applications include power regulators and controllers, exchange converters, optical systems. Industrial Power applications includes high-power transistors, arrays, solid-state relays.
LED PCB Solutions

What technological advancements were we trying to achieve?
The technological objective of this project was to develop a new LED module for high luminous efficacy.
Historically, the state of the art in MCPCB based LED technology consisted of a metal core base layer, covered with a dielectric layer (where the circuit is formed). Wires re manually soldered to the traces to achieve operational conductivity. The thermal conductive pillar for the LED modular array will improve efficiency and cross-platform design. With the current technology resistance arcing acts a limiting factor as high current LED drivers require 1500V (3 second interval). The dielectric layer limits the circuit due to the barrier it creates between the two layers establishing a thermal conductivity of 200W/K*m. Additionally, significant portions of light is typically reflected by the surface of the waveguide and is absorbed and scattered by substrate as the dielectric layer, the electrode pads and wires covering the substrate have very low reflectivity limiting the luminous efficiency to 60 Lumens/W.

To overcome these constraints, Cofan sought to develop the following:

- New thermal management technologies in Metal Core Printed Circuit Board (MCPCB) capable of achieving a conductivity of 320 W/m-K. This new module technology would withstand a 1500V exposure for a period of 3 seconds.

- Integrate the new LED module with top reflective surface layer with a waveguide structure to improve luminous efficiency to 90 Lumens/W wit new technology to combine metal core technology with an aluminum reflective panel.

However, this proved to be challenging as increasing the conductivity required the removal of burr induced conducing tracts formed through the mechanical forces present through drilling. For this reason Cofan needed to redevelop a method to form the necessary etched cavities. Additionally, Cofan encountered challenged in the new module with the top reflective surface as Cofan was uncertain of the optimal bonding procedure involving the pre-impregnated glass fiber material with two sandwiching layers, total of three layers, as Cofan had never bonded more than two layers.

If successful, this technology could be applied to light-emitting diodes (LED) lighting mounted on a surface module, maintaining high thermal conductivity while performing in a high current driver application. Cofan seeks to develop a module that can essentially be handled as a plug-and-play LED device while increasing the lumen output the overall efficiency and applicability increase drastically.

Through this project Cofan advanced their scientific knowledge in the field of electrical engineering by developing a LED module to improve the thermal conductivity, luminous efficiency and the technology of the MCPCB to effectively withstanding a 1500V exposure for 3 second duration and sought to improve luminous efficacy to upwards of 90+Lumens/W.

What technological obstacles did we have to overcome?
The technological obstacles encountered in the fiscal year, revolved around developing a high current driver, high luminous efficacy LED module combining new Metal Core PCB heat dissipationo technologies with a new aluminum reflective panel integrated with the Metal Core PCB.
Specifically, Cofan encountered the following technological obstacles in the fiscal year:

Dielectric strength (resistance to arcing) and consistency of epoxy flow
- Cofan needed to alter the drilling process when forming small cavities intended for current insulation to prevent the formation of undesirables conducting tracts. Initial attempts of using a drilling process resulted in the development of copper burrs which essentially created conducting tracts, which compromised dielectric strength; due to the substantial mechanical forces and over-stressing yields displaced on the copper plating which was present during this operation.

Voids in the substrate layer and lamination impacts
- Cofan needed to establish a correlation between the change in Cu and the PCB edge distance relative to the BDV in the air, to actively prevent the failures due to voids in the non-conductive epoxy resin. Initial attempts using a chemical etching process resulted in the formation of unpredictable voids forming within the epoxy which decreased the dielectric strength significantly.

Optimal cavit profile for epoxy resin flow
- Cofan was uncertain of the optimal size and shape of the cavities required to allow for consistent resin flow to minimize voiding. As such, experimentation with various pocket sizes within the cavity was required to allow for consistent resin flow to minimize voiding. As such, experimentation with various pocket sizes within the cavity was required to improve the initial flow of the epoxy resin and thereby preventing formation of voids and air bubbles. The initial cavity pocket size of 0.109” failed to allow the epoxy to initially flow into the barrel and prevent voids.

LED reflective panel to improve luminous efficacy
- Cofan was uncertain how the mechanical processes to form the reflective panel and the distortions in the panel would impact the laminate adhesion as well as the overall luminous efficacy of the assembled module. Initial attempts using the reflective panel resulted in yield rates below 50% due to leakage of pre-impregnated glass fiber material into the LED pocket, resulting in contamination.

What work did we perform in last year to overcome those technological obstacles?
Dielectric strength (resistance o arcing) and consistency of epoxy flow
Initially Cofan theorized, utilizing a drilling process to maintain material properties by avoiding substantial mechanical forces and stresses preventing the formation unwanted conductor tracts. To do so Cofan experimented by drilling small cavity hole for the current insulation on the copper trace. However, with this process, Cofan observed that there was a strong presence of copper burs which compromised the dielectric strength resulting in the circuit unable to withstand resistive arcing at/exceeding 1500V for the duration of 3 seconds. In attempts to resolve this issue and inherently minimize the probability of resistance arcing, Cofan hypothesized that a chemical process would reduce the level of induced stress and deformation (through a cold process) in order to maintain the original properties while preventing the formation of burs. A hydrochloric acid and copper sulphate based formulation was experimented with as an etching solution; the chemical was intended to remove the copper silvers quickly to ensure no damage occurs to the copper base. Testing this theory Cofan immersed the copper board into the solution. Cofan observed a buildup of cupric chloride, where the disproportional reaction took over cuprous chloride. With this strategy, Cofan observed improved consistency with the high-pot tests.

Voids in the substrate layer and lamination impacts
However, with this new etching strategy Cofan also observed higher failure rates as unpredictable voids began to form on the epoxy resin, compromising the dielectric strength of the trace. Cofan performed further testing to develop a correlation between the change in Cu and he PCB edge distance relative to the BDV in the air, bounding the distance between 1mm-5mm. A series of 6 distances with 1mm increments and 1.5mm were tested, analysis of the results showed that distance between the Cu and PCB edge relative to the BDV (kV) had a linear correlation exhibiting potential optimal distances for curing of the epoxy based on a resin thickness of 200VDC/mm.

Shape – Thermal transfer takes place at the surface of the heat sink. Therefore, heat sinks should be designed to have a large surface area. This goal can be reached by using a large number of fine fins or by increasing the size of the heat sink itself.
Although a bigger surface area leads to better cooling performance, there must be sufficient space between the fins to generate a considerable temperature difference between the fin and the surrounding air. When the fins stand too close together, the air in between can become almost the same temperature as the fins, so that thermal transmission will not occur. Therefore, more fins do not necessarily lead to better cooling performance.

Surface Finish – Thermal radiation of heat sinks is a function of surface finish, especially at higher temperatures. A painted surface will have a greater emissivity than a bright, unpainted one. The effect is most remarkable with flat-plate heat sinks, where about one-third of the heat is dissipated by radiation. Moreover, a perfectly flat contact area allows the use of a thinner layer of thermal compound, which will reduce the thermal resistance between the heat sink and LED source. On the other hand, anodizing or etching will also decrease the thermal resistance.
Mounting method – Heat-sink mountings with screws or springs are often better than regular clips, thermal conductive glue or sticky tape.
For heat transfer between LED sources over 15 Watt and LED coolers, it is recommended to use a high thermal conductive interface material (TIM) which will create a thermal resistance over the interface lower than 0.2K/W Currently, the most common solution is to use a phase-change material, which is applied in the form of a solid pad at room temperature, but then changes to a thick, gelatinous fluid once it rises above 45°C.

Heat pipes and vapor chambers[edit]
Heat pipes and vapor chambers are passive, and have effective thermal conductivities ranging from 10,000 to 100,000 W/m K. They can provide the following benefits in LED thermal management:[3]

Aluminum-base copper clad laminate sheet ( AL CCL / MCPCB )
aluminum copper-clad laminate are one kind of metal core PCB's, made of aluminum ( 1060, 3303, 5052, 6061) as metal base layer, Prepreg as dielectric layer between circuit layer-copper and metal base, pressing under heat and pressure, formed up embryo sheet, then we film low temperature (100℃)/ medium temperature (180℃)/ High temperature(280℃) on the metal base side. Anodic oxidation process surface. Which have excellent heat dissipation, heat resistance, reliability, long life. Hard surface ensure circuit board molding burr easy control, mechanical processing high efficiency.
Thermal conductivity: 1w, 2w.

An LED driver is an electrical device which regulates the power to an LED or a string (or strings) of LEDs. An LED driver responds to the changing needs of the LED, or LED circuit, by providing a constant quantity of power to the LED as its electrical properties change with temperature. An LED driver is a self-contained power supply which has outputs that are matched to the electrical characteristics of the LED or LEDs. LED drivers may offer dimming by means of pulse width modulation circuits and may have more than one channel for separate control of different LEDs or LED arrays. The power level of the LED is maintained constant by the LED driver as the electrical properties change throughout the temperature increases and decreases seen by the LED or LEDs. Without the proper driver, the LED may become too hot and unstable, therefore causing poor performance or failure.
Types of LED Drivers

Single Layer Metal Core PCB

A simple layer single sided MCPCB consists of a metal base (usually aluminum, or copper alloy), Dielectric (non-conducting) Layer, Copper Circuit Layer, IC components and solder mask.

The prepreg dielectric provides excellent heat transfer from the foil and components to the base plate, while maintaining excellent electrical isolation. The base aluminum/copper plate gives the single-sided substrate mechanical integrity, and distributes and transfers the heat to a heat sink, mounting surface or directly to the ambient air.

The Single-Layer MCPCB can be used with surface mount and chip & wire components, and provides much lower thermal resistance than FR4 PWB. The metal core provides lower cost than ceramic substrates, and allows much larger areas than ceramic substrates.

Double Layers Metal Core PCB

Double layers MCPCB is consisting of two layers of copper conductor, put them on same side of metal core (usually aluminum, copper or iron alloy). The metal base is on the bottom of whole MCPCB, which is different from double sided MCPCB(the two copper layers were put on the each side of metal core respectively), and you can only populate SMD on top side.

Different with Single layer MCPCB, 2 layers MCPCB requires an additional pressing step to laminate the imaged thermal conductive laminate and metal core (also known as metal base) together.

Compared with normal FR4, this sturcture need more technology and experience on laminating of two layers together with metal core.

The processing steps of the MCPCB with the metal base embedded in the PCB are comparatively complex as hole plugging is required after primary drilling on the metal base in order to isolate it from the circuitry.

Double Sided Metal Core PCB

It also has same two layers of copper conductor like Double layers MCPCB, but the metal core is in the middle of two conductor, so there're conductors (trace) on both sides of metal core, and were connected to each other by Vias. So we named it "Double sided MCPCB", and you can populated SMD on both top and bottom.

Different with Single layer MCPCB, double sided MCPCB also requires an additional pressing step to laminate the imaged thermal conductive laminate and metal core (also known as metal base) together. But sometimes, some raw Metal Clad material vendor will supply board material which already laminated.

One of the main reasons why you would avoid fr4 vs. a ceramic circuit board or other MCPCB board has to do with heat transfer. Metal cores like aluminum nitride and beryllium oxide are extremely thermally conductive. fr4 PCB material is not. If you are using your boards in applications where heat is a real issue, like LED lighting, you will probably want to move away from standard fr4 boards towards ceramic boards or other metal core PCBs, as metal core boards can more easily carry excess heat away from hot spots that can ultimately damage the board by reducing the life of semiconductor junctions.
Other metal core PCB materials in addition aluminum and beryllium can include copper and steel alloy. Steel alloys provide a stiffness that you will not get with copper and aluminum, but are not as effective at heat transfer. Copper has the best ability to transfer and dissipate heat as part of your printed circuit boards, but it is somewhat expensive — so companies on a budget producing or purchasing many printed circuit boards will often opt for aluminum as a cheaper but still highly effective heat-dissipating alternative to fr4 boards.
Aluminum Printed Circuit Boards
For most businesses, the most cost-effective solution will be metal core printed circuit boards with an aluminum base. You get good rigidity and thermal conductivity at a more reasonable price. For this reason, if you order metal core printed circuit boards and do not specify copper, you can usually expect an aluminum core.
How Metal Core PCBs Dissipate Heat
The reason metal core PCBs are so much more effective at dissipating heat than fr4 boards is due to their thermal conductivity dielectric material, which serves as a thermal bridge from the IC components to the metal plate, automatically conducting heat through the core to a heat sink. If you have fr4 boards, you must add a topical heat sink to transfer heat through the board or it will create potentially damaging hotspots.
Other Advantages of MCPCBs
In addition to preventing hot spots, a metal core PCB’s thermal conductivity properties also result in less thermal expansion and, as a result, greater dimensional stability. Thermal expansion can cause different layers of the board to take on different shapes or sizes, affecting the integrity and functionality of the board. Protection from thermal expansion is desirable.

Compared with normal FR4, this sturcture need more technology and experience on laminating of two layers together with metal core.

Multi Layers Metal Core PCB

Just like FR4 PCB, we can also make boards with more than 2 layers of traces and we named it "Multi Layers MCPCB". The structure is similar with FR4 Multi Layers, but it much more complex to make.

You can populated more components on the boards, put signal and ground layer into seperated layers, to achieve better performance in electrical performance.

Compared with normal FR4, this sturcture need more technology and experience on laminating of more than two layers together with metal core and the cost is much higher than 2 layers MCPCBor double sided MCPCB.

There are several different kinds of LED drivers. At Future Electronics we stock many of the most common types categorized by output current per channel, supply voltage, output voltage, maximum switching frequency and packaging type. The parametric filters on our website can help refine your search results depending on the required specifications.
The most common sizes for supply voltage are 2.3 to 5.5 V, 2.7 to 5.5 V and 3 to 5.5 V. We also carry LED drivers with supply voltage up to 630 V. The output current per channel can be between 250 µA and 50 A, with the most common chips having an output current per channel of 20 mA, 25 mA and 100 mA.
LED Drivers from Future Electronics

Future Electronics has a complete selection of LED drivers from several chip manufacturers that can be used as a high power LED driver, constant current LED driver, RGB LED driver, dimmable LED driver, 24v LED driver, in an LED driver IC (integrated circuit) or LED driver board as well as for any circuits that might require LED driver chips.
Future Electronics has a complete selection of LED drivers from several chip manufacturers that can be used as a high power LED driver, constant current LED driver, RGB LED driver, dimmable LED driver, 24v LED driver, in an LED driver IC (integrated circuit) or LED driver board as well as for any circuits that might require LED driver chips.

- High thermal conductivity (a ;line up with maximum conductivity of 8W/mK)
- High reliability (voltage resistance, heat resistance, and heat shock resistance and durability)

In the field of power hybrid ICs, progress is being made every day in terms of miniaturization, higher degree of integration and higher power. These substrates require a higher degree of heat dissipation as well as higher reliability and processing power than their predecessors. DENKA has released a series of high thermal-conductivity materials such as “DENKA THERMALLY CONDUCTIVE SHEET” from this very standpoint.

“DENKA HITT PLATE” is a metal circuit board with high thermal conductivity, which DENKA has developed using our high thermal-conductivity technologies, consisting of an aluminum base, an epoxy-based insulation layer with a high inorganic content filler demonstrating high thermal conductivity, and a conductive foil, thereby realizing thermal resistance equivalent to, or less than that of an alumina ceramic substrate.

They are used in a wide variety of applications, including air conditioner inverters, stereo amplifiers, automobile and motorcycle electrical devices, and power supplies for communications equipment.

Transport heat to a remote heat sink with minimum temperature drop
Isothermalize a natural convection heat sink, increasing its efficiency and reducing its size. In one case, adding five heat pipes reduced the heat sink mass by 34%, from 4.4 kg to 2.9 kg.[4]
Efficiently transform the high heat flux directly under an LED to a lower heat flux that can be removed more easily.[5]
PCB (printed circuit board)[edit]
MCPCB – MCPCB (Metal Core PCB) are those boards which incorporate a base metal material as heat spreader as an integral part of the circuit board. The metal core usually consists of aluminum alloy. Furthermore MCPCB can take advantage of incorporating a dielectric polymer layer with high thermal conductivity for lower thermal resistance.
Separation – Separating the LED drive circuitry from the LED board prevents the heat generated by the driver from raising the LED junction temperature.
Thick-film materials system[edit]
Additive Process – Thick film is a selective additive deposition process which uses material only where it is needed. A more direct connection to the Al heat sink is provided; therefore thermal interface material is not needed for circuit building. Reduces the heat spreading layers and thermal footprint. Processing steps are reduced, along with the number of materials and amount of materials consumed.
Insulated Aluminum Materials System – Increases thermal connectivity and provides high dielectric breakdown strength. Materials can be fired at less than 600°C. Circuits are built directly onto aluminum substrates, eliminating the need for thermal interface materials. Through improved thermal connectivity, the junction temperature of the LED can be decreased by up to 10°C. This allows the designer to either decrease the number of LEDs needed on a board, by increasing the power to each LED; or decrease the size of the substrate, to manage dimensional restrictions. It is also proven that decreasing the junction temperature of the LED dramatically improves the LED’s lifetime.

Through further experimentation Cofan identified the difficulty was arising due to the application process of the non-conductive epoxy into the insulation cavity as it contained a copper base contamination. Cofan observed the cavity barrels were too deep to avoid the air trap at a base thickness of 0.125”. To overcome this team experimented by securing the epoxy inside the barrel and implementing a vacuum bed effectively descend the epoxy resin to the base, during the screening process. Experimentations showed improvements in yield however, results were still considered poor as the failure rate was measured to be 25% alongside a lack of consistency. Upon further inspection Cofan was able to correlate the failure to the high degree of viscosity of the epoxy. To resolve this, Cofan experimented with the use of pre-treatment methods which enhanced the lamination by forming an oxide layer, increasing bond strength within the copper base, Using black oxide Cofan converted the surface of the material to magnetite(Fe3O4) which offered sufficient corrosion resistance. Testing this pre-treatment Cofan applied oxide layer on a single side of the copper base. Cofan performed a sequential process comprising of pre-clean,, water rinse, micro-etching, water rinse, black oxidation process, water rinse and finally a 60 degree baking process. Cofan experienced positive results as the pre-treatment increased the bond strength to an optimal degree, however, the epoxy still continued to form voids.

Sample Metal Boards
Click the image below for LED sample boards and board specifications.

Express PCB		Rigid PCB Rapid Prototype,24 hours
Fr4 PCB		prototype Lower to 15USD !
Rapid Prototype		Fr4 Rigid PCB Rapid Prototype China,

MCPCB		MCPCB Manufacturer China, Shenzhen
Aluminum PCB:		Aluminum Metal Core PCB manufacturing, Fabrication
Aluminum PCB:		single side, double side MCPCB, 0.5-5mm or more

Rogers 4350B		Rogers 4350,Rogers 4003 Manufacturing
Rogers 4350B		Rogers 4350B,4003C PCB Manufacturer
Ro4350B		Rogers High Frequency PCB Manufaturing China

Turnkey Services		Turnkey PCB Assembly Services,
Turnkey services		Print circuit board Manufacturing, Turnkey Services
Turnkey Assembly		Through Hole PCB components wave soldering Assembly

High power DC DC converter Aluminum mcpcb aplication

PCB Supplier Shenzhen, China, PCB Manufacturer, Turnkey services

Express PCB

Rigid PCB Rapid Prototype,24 hours

MCPCB

MCPCB Manufacturer China, Shenzhen

Rogers 4350B

Rogers 4350,Rogers 4003 Manufacturing

Turnkey Services

Turnkey PCB Assembly Services,

High power DC DC converter Aluminum mcpcb aplication