[introduction]Hot design is a crucial task, language of all sorts of among them regulation, skeletonize and complex equation let a person feel it appears constantly is an abysmal mystery domain; But the meaning that its design to integrated circuit nots allow to ignore however — after all, temperature is the element of the biggest environment of the invalidation in bringing about most semiconductor to be in actual applying. The life expectancy of component can lift as each degrees of temperature and shorten.

Hot design is a crucial task, language of all sorts of among them regulation, skeletonize and complex equation let a person feel it appears constantly is an abysmal mystery domain; But the meaning that its design to integrated circuit nots allow to ignore however — after all, temperature is the element of the biggest environment of the invalidation in bringing about most semiconductor to be in actual applying. The life expectancy of component can lift as each degrees of temperature and shorten.

The article will take you to discuss the issue of a few keys that attention needs in designing an engineer to design a process in heat deep. Specific for, we focusing high-power nitrogen changes gallium (GaN) parts of an apparatus and its are in actual application the relevant hot problem that faces.

Be aimed at the hot design of dependability

Hot design is a complex task, but among them also principle of a few foundations is worth to be discussed deep. Let us review above all in printed circuit board (PCB) on a few basic knowledge when using model to seal semiconductor.

In hot design process, the program of hot method is the element that wants a consideration above all; The quantity of heat that it produces for semiconductor offerred to lead to method of outside ambient airy. This hot method can pass ground connection solder commonly dish the bottom that crosses parts of an apparatus to enclose (if pursue,show 1 times) . Because this is in applied design, ought to choose those to be able to pass ground connection of parts of an apparatus piece quantity of heat from enclose the PCB with effective and derivative bottom.

Enclose in this kind in, because model seals function of compound heat conduction not beautiful, try from enclose coping to absorb caloric method not be successful; And may bring about node and raceway groove temperature again from coping refrigeration exorbitant, cause function of parts of an apparatus to drop thereby even invalidation.

Use the accurate method that discharge heat to ensure, when designing system or end item, the information that uses semiconductor supplier more to offer as far as possible and material (include S2P parameter and PCB Gerber file to wait) very important. For example, guide the placement of via is mixed found very crucial to raising component dependability from quantity of heat of the eduction in equipment — the specification of these types and guide the placement of via, the PCB Gerber that can offer in semiconductor supplier normally is found in the file.

Ground connection piece with PCB between solder attachment, should choose can efficient optimize medicinal powder hot high quality material. The position of via, size and style often optimize a principle to offer according to function by the supplier, because this answers,use below the guidance of the supplier. The position of via, style and kind are small to coming true of thermal resistance medicinal powder hot passageway has main effect. When use carbon fin, had better join its go up to the lowermost impedance method of IC node or raceway groove.

In addition, the thermal resistance of PCB and circuit board integral ply becomes direct ratio, heat conduction aperture also is one of factors that affect thermal resistance value. Accordingly, compressed to using square type is not had cite a base (QFN) enclosed high-power GaN parts of an apparatus, choose ply to be 8mil close Er normally (fine long hair inch) ultrathin PCB, reduce thermal resistance with the oldest rate. The hot property of PCB material still is in on circuit board by copper the influence of laid means.

Want to install quantity of heat the area of carbon fin to deliver to lower part, need to use at least medicinal powder hot aperture. Medicinal powder hot aperture is to be on circuit board the copper facing hole that drills, use at forming to arrive from layer of a copper the heat conduction passageway of next copper layer. Cupreous layer Yue Houyue is good, because it offerred admirable thermal conductivity, but use copper is more, cost is higher also.

In low power application, the number of plies that increases PCB is conducted to the heat of component have distinct effect. Double deck circuit board may be as high as 20 ° C with the difference in temperature between 4 circuit board, specific depend on copper comes loose planarly hot layout is designed (if pursue,2 are shown) .

Although to low power setting, increase PCB number of plies to be able to bring certain benefit, but can produce the result that be just the opposite to what one wished however in high power application. For example, in the application such as parts of an apparatus of high power of such as GaN, exceed 10 to fall to the circumstance of 15 tile in power especially, increase PCB number of plies to be able to increase thermal resistance not only, disturb heat possibly still to conduct method.

High-power GaN parts of an apparatus uses a note

Reach sheet in the light of GaN parts of an apparatus piece microwave integrated circuit (MMIC) when undertaking heating up an analysis, recommend use a kind of synthetic method; This kind of method makes full use of parts of an apparatus builds model, experience to measure (include Raman heats up miniature to resemble) and finite yuan of analysis (FEA) emulate, already was by the proof the most effective and the most accurate instrument. Once finish what base line heats up a model to build, can come through FEA the raceway groove temperature that essence of life allows to calculate level of parts of an apparatus and thermal resistance.

If cannot use miniature to pull graceful heat to become,resemble building a model with FEA, and can use only infra-red (IR) camera, must be clear that understanding IR becomes the confine that resembles going up in precision so. The dimensional resolution of IR camera is bigger than the grid length of FET raceway groove an amount class, and get exterior temperature all is worth for the area, far under temperature of actual highest raceway groove.

The applied group of proposal and supplier of GaN parts of an apparatus cooperates cheek by jowl, in order to ensure GaN parts of an apparatus is in your application with enough low temperature moves. Still can apply a group to obtain product whole to come loose from its hot model, the systematic level that brings into its you comes loose in hot model, run an environment with evaluating parts of an apparatus well and truly, the form that produces from this certainly then lukewarm or raceway groove temperature.

Raise the thermal conductivity in application

Be aimed at only naked piece application

Naked to GaN a component, should install its directly go up in the carbon fin stuff with good thermal conductivity or on intermediate support plate, use for example naked piece stick piece (Die-on-tab) means. When installation, should (preferential) solder of use gold Xi Gongjing or epoxy resin of tall thermal conductivity. Carbon fin is OK as compositive as component of below one class, also can use solder or electric epoxy resin with naked piece stick piece the structure installs the carbon fin that issueing one class package to go up directly.

Golden stannum solder has inferior thermal resistance value with a lot of thermal conductivity epoxy resin, and can bear heat up coefficient of expansion (CTE) break the stress that deserves to cause (often appear when GaN chip installation arrives on material of tall thermal conductivity) . It is very important to ensure dot of golden stannum solder does not have space, be in especially naked a valid area lower part. If use the condition with electric poorer epoxy resin to fall, silver-colored oar must even, without space, raise thermal conductance with utmost.

Not proposal general GaN is naked direct installation is in a power parts of an apparatus printed circuit board on, unless its installation is in metal of tall heat conduction piece (be like cupreous piece) on, in order to make sure enough heat is conducted.

GaN QFN and surface are stuck outfit enclose application

GaN QFN and surface are stuck outfit enclose package to be installed directly go up in PCB. These GaN amplifier are used in the application of medium power dissipation normally; No matter be successive wave (CW) mode or pulse application. In these setting, need uses copper to pledge heat conduction via will offer heat conduction way for systematic carbon fin. When the dimension that choosing via, position, type and copper facing are measured, should mature the function of integral heat conduction that optimizes PCB design.

Enclose to GaN QFN, the proposal falls PCB ply to lowest (be like 0.008 inches) , in order to maintain inferior thermal resistance. Those who make appliance has concentrated via array is thin model PCB is weighed particularly should, especially to high frequency GaN MMIC.

Heat conduction method is parts of an apparatus comes loose normally hot the most efficient way. Stick to QFN and surface outfit enclose amplifier, ensure it is very important to all be worth CW to heat up flux to be more than 1W/mm2 from the area that encloses bottom output. In addition, intense proposal is used set the PCB that buries cupreous piece, think systematic carbon fin offers good heat conduction way. In addition, exceed the application of 2 W/mm2 to any hot flux, must be in enclose lower part to set bury cupreous piece.

GaN copper facing (CP) enclose application with flange type

Transistor is enclosed in high-power GaN or enclose MMIC and carbon fin between, have good hot interface special key.

Enclose join undesirable it is a when bring about hot invalidation main reason. Below high power circumstance, qorvo suggests to use by heat conduction material (like indium piece or black lead film) make, ply is 2 to 4mil close Er (make an appointment with 50-100 μ M) hot interface material (TIM) ; Or, also can use ply to be 1 to 2mil close Er (make an appointment with 25-50 μ M) heat conduction creams or guide thermalization closes matter, enclothe whole enclose base area, the parts of an apparatus that so that install flange type,encloses.

There is a point to need to notice in the use of TIM: Conduct the result to win good heat, must bring to bear on enough pressure. When use heat conduction to cream or guiding thermalization closes matter, should ensure achieve at least of 80% enclothe rate.

Conclusion

Good hot design moves reliably to the spot very crucial; Produce component of many caloric high-power in the light of those especially, importance is more self-evident.

Design a technology through abiding by the heat that is based on optimal practice, engineers can ensure of systematic performance optimize, utmost ground reduces potential problem, prolong the service life of component as far as possible.

 (Origin: Qorvo semiconductor, author: David Schnaufer, technical mart transmits a manager)

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