Patent Description:
The designs of power electronic devices and systems are being continuously improved by becoming smaller in size and faster in switching frequency. The potential risk associated with these specific design improvements is an increase in power density and, consequently, a greater risk of thermal problems and failures. Typically, thermal conductivity is a material property that describes the ability of a material to conduct heat through the material. Conventional PCB materials such as FR4 have one of the lowest thermal conductivities and are not capable of meeting the continuously increasing demand of the thermal requirement of the high-power dissipation PCB. One of the current approaches to address this thermal dissipation problem is the use of a Metal Core Printed Circuit Board (MCPCB). However, even though an MCPCB has a higher thermal conductivity compared to an FR4 PCB, it still uses a thermal interface material (TIM) and a coldplate, which has a top plate between the source of heat and the cooling medium inside the coldplate. The TIM and the top plate of the coldplate are main a root causes that impede the cooling performance. Thus, the high-power density power electronics face challenges including how to improve the TIM layer, and how to maximize heat transfer at the top plate of the coldplate.

The conventional techniques have been considered satisfactory for their intended purpose. However, there is an ever-present need for improved systems and methods for cooling PCBs. This disclosure provides a solution for this need.

<CIT> discloses that an apparatus and related method for housing a light assembly apparatus includes a housing having a housing first end and a housing second end arranged along a central axis, the housing further includes a plurality of fins each having a fin first end and a fin second end, the plurality of fins forming a plurality of vents therebetween, each the plurality of fins has a curvature extending from the fin second end such that the plurality of fins converge towards the central axis proximate each fin first end, an endpiece proximate the housing first end and arranged proximate to the fin first end of each of the plurality of fins, the endpiece having a circular portion including a continuous circumference about the central axis, an electrical connector arranged proximate to the endpiece and arranged along the central axis, and a space arranged along the central axis proximate the housing second end and further configured with the plurality of fins and the plurality of vents arranged therearound, the space configured to, at least in part, house a light assembly.

According to an aspect of the invention, a printed circuit board (PCB) assembly is provided according to claim <NUM>.

There can be a thermal path defined through the PCB directly from the heat generating component into the plurality of pin-fins without passing through an intervening cold plate wall or thermal interface material (TIM) between the heat generating component and the plurality of pin-fins. The heat generating component can include a wide band gap (WBG) device selected from a group consisting of a GaN and a SiC MOSFET. A lid can be assembled onto the bottom side of the PCB, enclosing the pin-fins in a cooling channel defined between the lid and the PCB. A coolant medium such as a dielectric coolant fluid can be included in the cooling channel. The lid can include both hot and cold coolant paths. A sealing material can be included between the lid and the PCB for sealing coolant in the cooling channel.

The pin-fins can extend from a metal core of the PCB. The metal core can perform the role much as with a conventional FR4 core. Based on the metal core, more layers can be stacked up, e.g. starting with an aluminum core layer, a dielectric material layer can be stacked on which conduction layer can be stacked, on which a dielectric material layer can be stacked, on which a conduction layer can be stacked, on which a solder mask can be stacked. Each pin-fin can be joined to the metal core with an arc-welded weld joint. In the multi-layer PCB configuration, thermally conductive vias can extend through the conduction layer top for transferring of heat from the heat generating component to the pin-fins.

In the FR4 based PCB, each pin-fin in the plurality of pin-fins can extend from the top side of the PCB, through the FR4 material, and extends beyond the bottom side of the PCB to form a combined thermal via and pin-fin. Each of the pin-fins can be joined to the top side of the PCB with a solder joint. The heat generating component can be mounted to the top side of the PCB with a thermal pad or direct soldering between the heat generating component and at least one pin-fin in the plurality of pin-fins.

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an embodiment of a printed circuit board (PCB) assembly in accordance with the disclosure is shown in <FIG> and is designated generally by reference character <NUM>. Other embodiments of systems in accordance with the disclosure, or aspects thereof, are provided in <FIG>, as will be described. The systems and methods described herein can be used to provide direct pin-fin cooling for high power semiconductors in PCBs, for use with cryogenic or non-conductive fluid or the like.

This invention disclosure proposes a direct pin-fin cooling for a high-power PCB. This solves the classical coldplate problems associated with liquid cooling of high-power PCB such as inhomogeneous cooling due to the calorimetric heating up of the coolant, thermal interface material (TIM) related quality issues such as dry-out effects, high cost due to complicated metal coldplate structure, and low thermal conductivity due to a multi-layer structure. Among them, the dominant factor for decreasing cooling performance is that to transfer heat from a power device to a coldplate, a thermal via and a TIM are used. Even if the coldplate has a high cooling performance, the top plate of coldplate is one more layer in the heat transfer path. The TIM can have a low thermal conductivity. Thus, this disclosure provides a high-power PCB and a pin-fin direct cooling structure without additional coldplate structures and TIM. In this approach, a TIM and a top plate of coldplate can be omitted from the heat transfer path between the heat generating components and the coolant. Thus, the cooling performance can be improved because the thermal conductivity between a liquid coolant and a power device is increased.

A first aspect is the metal core PCB (MCPCB) based pin-fin direct cooling as shown in <FIG>. In this structure, all MCPCB fabrication can be completed using conventional processes, e.g. this structure can be made in conventional manufacturing facilities without having to utilize specialized manufacturing. The metal core plate can be used for pin-fin structures. To increase the heat transfer coefficient, an Arc-Welding Technology (AWT) can be used to form cooling structures to a pin-fin base plate. The metal core plate has a plurality of pin-fins and cooling liquid flows directly into the pin-fin area. The pin-fin cross-sectional shape can be round, square, or any other suitable pin shape. Square pin-fin shapes are suitable for achieving high thermal conductivity. However, any type of pin-fin shape can be used. The final step is to provide a bottom cover or lid, which can be of a polymer material. This cover or lid structure can provide potential benefits in terms of flexible shaping, light weight and low thermal conductivity from coolant to ambient. In addition, the MCPCB has high voltage dielectric layer, e.g. 6kV insulation voltage. Thus, it has a high reliability in terms of partial discharging and high voltage insulation.

Another aspect is shown in <FIG>, which shows the FR4 based pin-fin direct cooling structure. This replaces the thermal vias, e.g. as in <FIG>, with long copper pillars. In this case, the copper pillar also used as a pin-fin. This approach can improve thermal conductivity dramatically compared to traditional cooling schemes. However, the electrical insulation may not be guaranteed if the copper pillar is directly connected to the thermal pad of power device (e.g. GaN or SiC) and a thermal pad is to be connected to source connector of a power device. Thus, this approach must be used with caution regarding partial discharging and low high-voltage insulation. Even if one uses a high voltage insulated thermal pad between a power device and a thermal pad, on cannot guarantee a partial discharge. Thus, the structure shown in <FIG> may be best suitable for lower voltage applications.

A third aspect is the double-sided pin-fin cooling structure shown in <FIG>. The basic concept is same as shown in <FIG>, but could also be applied to the structure of <FIG>, with a little modification that is the polymer cover or lid has PCB mounting structures on both sides.

A fourth aspect is the assembly process, as shown in <FIG>. This process has a potential benefit in an easy fabrication method and an easy assembly process. The first step is to assemble a cooling pin-fins on the metal core plate or PCB through holes. The second step is to assemble a polymer cover or lid to the PCB. In order to minimize a leaking, a laser-cut adhesives material can be used, such as Indium. In addition, a low temperature sealing materials can be used for cryogenic liquid coolant.

Potential benefits are as follows: high power density and reduced package thickness, good thermal performance, homogeneous cooling by direct pin-fins, no thermal interface material (TIM), so no dry-out effects, high thermal conductivity by omitting TIM and omitting a top plate of the traditional coldplate, light weight provided by polymer cover or lid structure and omitting the top plate of the traditional coldplate, and low-cost by polymer coldplate and being able to make use of existing fabrication processes and equipment.

With reference again to <FIG>, a printed circuit board (PCB) assembly <NUM> includes a PCB <NUM> with heat generating components <NUM> mounted on a top side <NUM> thereof. A plurality of pin-fins <NUM> extend away from the PCB <NUM> on a bottom side <NUM> of the PCB <NUM> opposite from the heat generating components <NUM>.

There is a thermal path defined through the PCB <NUM> directly from the heat generating components <NUM>, into the plurality of pin-fins <NUM>, which can release heat into a coolant, without passing through an intervening cold plate wall or thermal interface material (TIM) between the heat generating components <NUM> and the plurality of pin-fins <NUM>. This direct cooling thermal path can be filled with coolant <NUM>. The heat generating components can include a wide band gap (WBG) device, such as a GaN or a SiC MOSFET.

A cover or lid <NUM>, e.g. of a polymer material, is assembled onto the bottom side <NUM> of the PCB, e.g. using fasteners <NUM> as indicated in <FIG>, enclosing the pin-fins <NUM> in a cooling channel <NUM> defined between the lid <NUM> and the PCB <NUM>. The cooling channel can be filed with coolant <NUM> such as dielectric coolant fluid, which is labeled in <FIG>. A sealing material <NUM> can be included between the lid <NUM> and the bottom side <NUM> of the PCB <NUM> for sealing coolant <NUM> (labeled in <FIG>) in the cooling channel <NUM>. As indicated in <FIG>, the lid <NUM> can include pin-fin holes or receptacles <NUM> for receiving the ends of the pin-fins <NUM>.

The pin-fins <NUM> extend from a metal core <NUM> of the PCB <NUM>. The metal core is a bottom layer of the PCB <NUM>. The metal core <NUM> is a core of the PCB <NUM> upon which more layers can be stacked up, e.g. starting from an aluminum core layer, on which a dielectric material layer can be stacked, on which a conduction layer can be stacked, on which a dielectric material layer can be stacked, on which a conduction layer can be stacked, on which a solder mask can be stacked. Each pin-fin <NUM> is joined to the metal core with an arc-welded weld joint <NUM>. Thermally conductive vias <NUM> extend through the PCB <NUM> from the top side of the PCB <NUM> toward the metal core <NUM> for conduction of heat from the heat generating components <NUM> to the pin-fins <NUM>.

With reference now to <FIG>, a similar assembly <NUM> is shown wherein the PCB includes an FR4 material, and does not have a metal core <NUM>. Each pin-fin <NUM> extends from the top side <NUM> of the PCB <NUM>, through the FR4 material <NUM>, and extends beyond the bottom side <NUM> of the FR4 material <NUM> to form a combined thermal via and pin-fin <NUM>. Each of the pin-fins <NUM> is joined to the top side <NUM> of the PCB <NUM> with a solder joint <NUM>. The heat generating components are mounted to the top side <NUM> of the PCB <NUM> with a thermal pad <NUM> or direct soldering between the heat generating component <NUM> and at least one pin-fin <NUM> in the plurality of pin-fins <NUM>. <FIG> shows steps in assembling the assembly of <FIG>, which are similar to those described above with respect to <FIG>.

Claim 1:
A printed circuit board (PCB) assembly (<NUM>) comprising:
a first PCB (<NUM>) with a first heat generating component (<NUM>) mounted on a top side (<NUM>) thereof; and
a first plurality of pin-fins (<NUM>) extending away from the first PCB (<NUM>) on a bottom side (<NUM>) of the first PCB (<NUM>) opposite from the first heat generating component (<NUM>),
characterised in that the PCB assembly (<NUM>) further comprises:
a second PCB (<NUM>) with a second heat generating component (<NUM>) mounted on a top side (<NUM>) thereof;
a second plurality of pin-fins (<NUM>) extending away from the second PCB (<NUM>) on a bottom side (<NUM>) of the second PCB (<NUM>) opposite from the second heat generating component (<NUM>); and
a sidewall component (<NUM>) assembled between the bottom side (<NUM>) of the first PCB (<NUM>) and the bottom side (<NUM>) of the second PCB (<NUM>) to enclose the first and second pluralities of pin-fins (<NUM>) in a cooling channel (<NUM>) defined between the sidewall component (<NUM>) and the first and second PCBs (<NUM>, <NUM>).