Designing With Plastic RF Power Transistors White Paper
Freescale SemiconductorWhite PaperRFPLASTICWPRev. 2, 9/2015Designing with Plastic RF PowerTransistorsBy: Dan Leih, Leonard Pelletier and Mahesh ShahRFPLASTICWP White Paper Rev. 2, 9/2015 , 2014–2015. All rights reserved.Inc.1
Designing with Plastic RF Power TransistorsAbstract: This white paper shows the main benefits of RFpower plastic packages and provides recommendationson PCB layout, mounting and soldering techniques tocreate a robust as well as cost-effective design solutionusing over-molded plastic RF power devices.IntroductionFreescale has a legacy of manufacturing high power RFdevices stretching back more than five decades. Over thattime, packaging technology has evolved along with the wafertechnology packaged inside. In the past decade, the shift toplastic packages has accelerated in the high volume wirelesssegment. Today, almost all pre--driver and driver stage devicesand most output stage RF power devices are available in plasticpackages. Other RF power market segments are now movingto take advantage of the benefits of plastic packaging for highpower RF applications. Freescale is the leader in high power RFpackaging and has been making high power RF LDMOSdevices using plastic packages since the mid--1990s. Morethan 200 million devices using plastic packages have beenmanufactured in the past 15 years.Six Main Advantages of Plastic PackagesFor many semiconductor products, plastic long ago emergedas the package technology of choice. Especially for commodityproducts such as small signal transistors or memories, plasticoffered low--cost encapsulation that was easily scaled to highvolumes. For RF power amplifiers, plastic packaging wasdeveloped primarily to address certain performance limitationsinherent in ceramic devices. The main benefits of plasticdevices are sixfold.Improved Thermal PerformanceThe biggest advantage of using plastic packaged parts is theimproved thermal performance. Plastic packages use a copperheat spreader on which the die is mounted. Copper is one ofthe best thermal and electrical conductors, with its thermalconductivity close to 350–400 W/m-K depending on the copperalloy used. In comparison, air cavity packages use exoticmaterials, such as a copper--based laminate heat spreader.The thermal conductivity of the copper--based laminatematerial is close to 250 W/m-K. When the die is mounted on acopper heat spreader, there is a reduction of 15–20% in thethermal resistance compared to when the die is mounted on aircavity packages with a copper--based laminate heat spreader.Tighter Dimensional TolerancePlastic packaged parts have tighter dimensional tolerancesthan ceramic parts. Key dimensional specifications on a plasticpackaged part (e.g., seating plane height) have tolerances onthe order of 0.003 ( 0.076 mm) or better. The air cavitypackages have tolerances typically in the range of 0.005 ( 0.127 mm) or larger. These tighter dimensional tolerancesare a natural feature associated with the manufacturingprocess used to build plastic packages.Second-level Assembly ReliabilitySecond-level assembly reliability is an inherent advantage ofusing plastic parts. As previously mentioned, plastic packagesuse a copper heat spreader while air cavity packages use acopper--based laminate heat spreader. Thus, plastic packagesprovide much less CTE mismatch at the solder joint between theleads and the PCB, or between the heat spreader and the coinor pallet in which it is soldered, than air cavity packages. Thisimproves the solder joint reliability significantly. In addition, theabsence of gold material eliminates any issues related to goldembrittlement of the solder joint.More Power in Lighter PackagesRF plastic power transistors weigh less than the alternativeair cavity package options. Additionally, because of the betterthermal performance of plastic packages, more power ispacked in a plastic package than in an air cavity package of thesame size. For comparison, the highest power device withFreescale’s Airfast technology in an OM-780 plastic packagehas a 282 W P1dB power output capability. When the highestpower device with the same Airfast die technology is packagedin the same-sized NI-780 air cavity package, it is only capableof a 260 W P1dB power output. The total weight of the NI-780package is 4.6 g, while the OM-780 package weighs 3.1 g. Withthis weight differential, plastic packages can be a key factor insupport of the military directive of creating replacementplatform designs that are lower in size, weight, power and cost(SWaP-C) than existing solutions.Multi--stage RFIC CapabilityFinally, one of the faster-growing RF power product areas isin the design and development of multi-stage RF integratedcircuits on silicon. These RFIC devices not only have muchhigher gains than single-stage air cavity package devices, theyalso have added features, such as 50 ohm input and output,DC-blocked input matching, and inter-stage matching anddecoupling. Most contain a temperature tracking andcompensating feature. These RFIC devices have gains in the33 to 36 dB range and power levels as high as 275 W. Due tothe increased feature set associated with most RFIC powerdevices, they need the multi-lead package styles that are onlyavailable in the over-molded plastic package option. Theover-molded plastic packages are more amenable toincorporating multi-lead configuration than air cavitypackages.Correct Design Techniques for Creating RF PowerAmplifiers with Plastic TransistorsIn addition to the electrical design of the PA, keyconsideration should also be placed on how the RF high powerdevice will be mounted in the next assembly. The mounting ofthe RF power device and the interface used with the devicehave significant influence on the cost and on the performanceof the amplifier. This is not unique to plastic packages, butapplies to all high power RF devices. Due to tighter tolerances,plastic parts are more amenable to automated manufacturingprocesses such as pick--and--place and surface--mount reflowcompared to air cavity parts.Mounting Options and Heat Removal: Surface--mount orthrough the PCB?When designing with Freescale RF power plastic devices,one of the first decisions is whether to use the surface--mountcapabilities of the plastic package options and mount the RFdevice on the top of the PCB over a grounded via pattern, orto choose a through-the-PCB option with the RF power devicemounted directly onto the metal coin or pallet.RFPLASTICWP White Paper Rev. 2, 9/20152Freescale Semiconductor, Inc.
Designing with Plastic RF Power TransistorsThe device source contact is also the metal flange at thebottom of the package in both air cavity and over-moldedplastic packages. The source contact functions as bothelectrical ground and thermal ground. Thus the assemblydesign needs to provide for a heat-dissipation path through thebottom of the device to the ultimate thermal sink.There are two options for the heat removal: one is the use ofa via farm pattern, and the second is the use of a metal coin orpallet. The via farm has higher thermal resistance than themetal coin or pallet. However, the via farm has an advantagewith regard to cost: the RF PCB has many ground vias, so theaddition of a few more closely spaced vias in the source padof the RF PA (power amplifier) device will have almost no costimpact, while the addition of coin or pallet will have asignificantly higher cost impact.The decision to use a via farm or a metal coin or pallet forheat removal comes down to whether the use of a via farm canstill keep the device junction temperature within the rangewhere the device reliability still provides significant margin overthe lifetime expectations. If the increase in maximum dietemperature under worst-case operating conditions still meetsthe overall design longevity requirements, then a surface-mount option is usually the most cost-effective solution.A rule of thumb is that if the device has a power dissipationof 50 W or below, and the PCB thickness is 2.0 mm and below,then it is possible to mount this device in a surface--mountconfiguration. If the PCB thickness is greater than 2.0 mm, thenthe power dissipation capability through a via farm with thedevice in a surface--mount configuration will be lower.If the RF PA device cannot be surface mounted using the gullwing packages, an alternative is to use the device with straightleads and to mount it as reflow in cavity, as shown in Figures 2and 3. The cavity can be incorporated into the PCB in two ways:either as a coin or as a pallet. The choice is primarily driven bycost and size. If the PA board is small and compact, then apallet may be a good option. If the PA board is large comparedto the size of the RF device, then a coin with cavity will mostlikely be a cost--effective option.Choosing between Gull Wing and Straight LeadedPackagesThe PQFN, QFN, SOT-89, PLD-1.5 and PLD-1.5W packagestyles are leadless packages, and they are available only assurface--mount components, as shown in Figure 1. The largerplastic package options, such as the TO and OM, have twomounting options available: a surface--mount option with gullwing bent leads and a through-PCB option with straight leads.Freescale’s RF power devices in TO and OM packages aregenerally available in both gull wing and straight leadedoptions, providing customers with appropriate choices.SOT--89APLD--1.5WFigure 2. Example of a Through-PCB, Straight Leaded,Soldered Assembly MountingQFN 4 4Figure 3. Example of a Through-PCB, Straight Leaded,Over-molded Plastic RF Power Device, TO--270-2SOT--89A on PCBQFN 6 6 on PCBFigure 1. Examples of Surface--mount PlasticRF PackagesThere are three main factors to consider when choosingbetween gull wing and straight leaded packages: Overall RF power capability of the RF device Impact of power capability on junction temperature andcostFor customers who do not want to perform reflow mountingof RF power devices, the over-molded plastic package iscapable of clamping down into the cavity with only the leadssoldered to the PCB. The bolt-down or clamp-down methodsof assembling an RF power device will negatively affect theperformance to some extent. This performance loss is notrelated to just plastic RF power packages, but is also seen inair cavity packages. This has to do with the lower thermalinterface resistance of the soldered device and the improvedelectrical contact of the soldered interface. Figure 4 shows anexample of the same package mounted in all threeconfigurations. Thickness of the PCB when considering system-levelthermal resistanceRFPLASTICWP White Paper Rev. 2, 9/2015Freescale Semiconductor, Inc.3
Designing with Plastic RF Power Transistorssolder mask material. (Contrary to general belief, solder fillingof via holes does not improve the thermal performancesignificantly.)Gull wing devicesurface mountedon top of PCBSoldered into thecavity of the PCBwith coin or palletClamped into theheatsink withopening in the PCBFilled, planarized, and plated via holesAnother approach to fill the via hole is with the use of materialsuch as conductive epoxy that will be planarized and cured andthen plated over. This process requires the use of silver-filledepoxy material specifically designed for this application, andthen two process steps are added: planarization and platingover again. This adds to the cost, but yields a full metalized padthat is coplanar with the PCB top. A cross section of such afilled via structure is shown in Figure 6.Figure 4. Three Different Ways to MountRF Power PackagesVia Farm DesignThe use of via holes under a device as a heat dissipationpath is one common extension of the via hole technique in thePCB industry, where heat removal from the device through thePCB thickness is important. There are three different versionsof via construction that are most common in the industry.Unfilled via holesThe cheapest approach is the use of unfilled via holes in thePCB. Figure 5 shows an example of the unfilled via structure.Figure 6. Example of a Filled, Planarized andPlated Via HoleA Common Assembly Method for Surface--mountApplicationsFigure 5. Example of Unfilled Vias under aPQFN DeviceThe concern with unfilled vias, as seen in Figure 5, is ofmolten solder being drawn into the via hole during the reflowprocess. When the solder is drawn into the via hole, it willamount to a loss of solder volume available for the solder jointof the device, which can result in voids under the device. InFigure 5, the solder is drawn into the via hole, but the soldervolume lost is small. If the solder volume drawn into the via holeis larger, there is a possibility that the solder could reach all theway to the bottom via hole and collect on the other side of thePCB. If this happens, it will interfere with the bolting of the PCBonto the heatsink housing.Plugged via holesOne way to overcome this issue is to prevent the path of thesolder from being drawn into the via holes by plugging them.There are multiple options for what material to use for filling thevia holes. One option is to prefill the via holes with soldermaterial. Another option is to fill the via holes with epoxymaterial, either conductive epoxy or non-conductive epoxy.The most economical approach is to fill the via hole with theThe design of the via hole structure is an integral part of aheat dissipation method for high power devices, whether theyare in plastic or air cavity packages. The key is to get the mostcopper area under the device heat spreader as possible. Adiamond or staggered pattern is likely to yield a larger numberof via holes than a square pattern. In addition, smaller-diametervia holes may be more effective than larger-diameter via holesdue to the ability to pack more via holes, and eventually morecopper, into the area. The general assembly process steps forthe surface mount assembly method are available in Freescaleapplication note AN1949.If customers are interested in reflow in a cavity stylemounting of the RF power devices, the plastic packages arealso amenable to this type of mounting. The general instructionto develop a reflow in a cavity style design and assembly canbe accomplished by following the details provided in Freescaleapplication note AN1907.If customers choose to sacrifice RF performance slightly butprefer a bolt-down type assembly mounting, they can still usethe leaded over-molded packaged devices in a clampedconfiguration. The general instructions to develop this type ofdesign are provided in Freescale application note AN3789.For surface--mount applications utilizing either the leadlessPQFN, QFN, SOT-89, PLD-1.5, and PLD-1.5W packageoptions or the gull wing formed RF power transistors, the mostcommon assembly method is to screen print a solder pastepattern, pick and place the RF components along with everyRFPLASTICWP White Paper Rev. 2, 9/20154Freescale Semiconductor, Inc.
Designing with Plastic RF Power Transistorsother solder component on the PCB, and then reflow it in amulti-zone convection furnace. The solder mounting has toprovide a good consistent thermal and electrical contactbetween the package source contact and heatsinks. Goodsolder joints with minimum and distributed voids provide a lowelectrical and thermal resistance interface between the backside of the device ground and the heat sinking pad on the PCBvia pattern. This soldering process does not have to be perfect;the defectivity is measured by performing either sonoscaninspections or X-ray inspections. Solder imperfections willshow up as voids on the solder interface, where either the fluxwas not completely boiled off, or the solder paste failed to fullywet both surfaces. The maximum voiding that is acceptable tothe customer is based on the customer’s design limit andprocess capability. Overall IPC (Association ConnectingElectronics Industries) workmanship guidelines recommend a25% total voiding in the solder joint at heatsink. Whether anindividual design is capable of conforming to this criteriondepends on the customer’s design.package options. Also, solder mounting of RF high powerdevices tends to reduce the junction temperature, whichresults in better device performance as well as increasedMTTF. By following a few simple design guidelines that havebeen outlined in this paper and in various Freescale packagingapplication notes, one can create a simple, robust, repeatable,reliable, and cost-effective amplifier design.Terminology Definitions FIT — Failure in time (failures in trillion hours). Flange or heat spreader — The exposed metal, primarilycopper, part of the plastic package. The die is attached tothe top of the heat spreader and the exposed platedbottom is soldered to the carrier. Heatsink — The carrier that is typically bolted to a finnedheatsink. The heatsink forms the part of the thermal paththat carries heat away from the device and to the coolingair.Reliability of Plastic and Air Cavity Transistors Mil — Equal to 0.001 inches.Over the years, as part of Freescale’s reliability tests andqualification efforts for various devices, 3.5 million devicehours have been accumulated at various temperatures in testconditions for over-molded plastic packages. Over the sametime frame, 3.0 million test hours have been accumulated atvarious temperatures in different test conditions for air cavitymetal-ceramic packages. Based on the accumulated testhours, and using the same statistical assumptions, failure intime (FIT) rate and mean time to failure (MTTF) werecalculated for both package platforms at various maximumjunction temperatures in field use conditions. The MTTF valuesat different temperatures in the operating regions are plotted asshown in Figure 7. From the data presented, both air cavity andover-molded plastic packages have close to 1,900 years ofMTTF at a maximum operating junction temperature of 150 C. MTTF — Mean time to failure.10000 Over-molded plastic packages (OM) — A packageencapsulates the die and consists of a mold compound,wire bonds, leads, and the heat spreader. OM packages — Freescale RF over--molded packagedesignation. PLD packages — Freescale RF over--molded packagedesignation. Power amplifier (PA) — An electronic assembly modulethat takes in the input signal, amplifies the signal, andfeeds it to the antenna. Power device — An RF power device, usually asilicon-based LDMOS discrete device, a multi-stage ICdevice, or a GaAs or GaN device.MTTF (YEARS) Printed circuit board (PCB) — The electricalinterconnection between the RF power devices and otherelectrical devices that are part of a PA. RFIC — Radio frequency integrated circuit device.Over--Molded1000 Size, weight, power and cost (SWaP-C) — A militarydirective. Transistor outline (TO) packages — Freescale RFover--molded package designation.Air CavityReferences100100150200250TJ, JUNCTION TEMPERATURE ( C)Figure 7. Comparison of MTTF Values versusMaximum Junction TemperatureSummaryRF PAs designed with Freescale’s RF power plastic devicesoffer many advantages over amplifiers made with air cavity1. Freescale Application Note AN1949, Mounting Method forthe MHVIC910HR2 (PFP-16) and Similar Surface MountPackages.2. Freescale Application Note AN1907, Solder ReflowAttach Method for High Power RF Devices in Over-MoldedPlastic Packages.3. Freescale Application Note AN3789, Clamping of HighPower RF Transistors and RFICs in Over-Molded PlasticPackages.RFPLASTICWP White Paper Rev. 2, 9/2015Freescale Semiconductor, Inc.5
Designing with Plastic RF Power TransistorsHow to Reach Us:Home Page:freescale.comWeb Support:freescale.com/supportInformation in this document is provided solely to enable system and softwareimplementers to use Freescale products. There are no express or implied copyrightlicenses granted hereunder to design or fabricate any integrated circuits based on theinformation in this document.Freescale reserves the right to make changes without further notice to any productsherein. Freescale makes no warranty, representation, or guarantee regarding thesuitability of its products for any particular purpose, nor does Freescale assume anyliability arising out of the application or use of any product or circuit, and specificallydisclaims any and all liability, including without limitation consequential or incidentaldamages. “Typical” parameters that may be provided in Freescale data sheets and/orspecifications can and do vary in different applications, and actual performance mayvary over time. All operating parameters, including “typicals,” must be validated foreach customer application by customer’s technical experts. Freescale does not conveyany license under its patent rights nor the rights of others. Freescale sells productspursuant to standard terms and conditions of sale, which can be found at the followingaddress: freescale.com/SalesTermsandConditions.Freescale and the Freescale logo are trademarks of Freescale Semiconductor, Inc.,Reg. U.S. Pat. & Tm. Off. Airfast is a trademark of Freescale Semiconductor, Inc. Allother product or service names are the property of their respective owners.E 2014–2015 Freescale Semiconductor, Inc.RFPLASTICWP White Paper Rev. 2, 9/20156RFPLASTICWPRev. 2, 9/2015Freescale Semiconductor, Inc.
Designing with Plastic RF Power Transistors By: Dan Leih, Leonard Pelletier and Mahesh Shah . process used to build plastic packages. Second-level Assembly Reliability Second-level assembly reliability is an inherent advantage of using plastic parts. As previously mentioned, plastic packages . plastic parts are more amenable to automated .
Plastic bottles are responsible for 15% of total plastic consumption in Austria.13 According to the new BMK study, 300,000t of plastic - including 49,000t of plastic bottles - were put on the market in 2018. In total, 1.6 billion plastic bottles are placed on the market every year, which equals 181 plastic bottles per Austrian.14
The Tide Turners Plastic Challenge is a global youth movement to fight plastic pollution around the world. It is designed to inspire young adults to reflect upon their plastic consumption, . Plastic Tide Turners Challenge Badge Toolkit Plastic Tide Turners Challenge Badge Toolkit. Toolkit. and . and a . plastic pollution. The 2021. India.
Combat Plastic Pollution Create Solution. PROBLEM STATEMENT 8.3 billion tonnes of plastic have been . 13 million tonnes of plastic enter ocean each year 1 million plastic bottles, 10 million plastic bags bought every minute 50% of consumer plastics are single use, and 10% of all human-generated waste is plastic 100,000 marine animals killed .
Introduction to Plastic Mold Design 19-3 Figure 19-2 Mold Design interface of Autodesk Inventor Importing Plastic Part in Mold Environment To import a model in the Mold environment, choose the Plastic Part tool from the Plastic Part drop-down of the Mold Layout panel in the Ribbon; the Plastic Part dialog box will be displayed, as shown in Figure 19-3.
Analysis of large plastic deformation of elasto-plastic solids Friction involves large plastic deformation. There are different ways of solving the deformation of elasto-plastic solids. are approximate solutions, can be very useful in engineering. One of the methods used is the slip-line field method, which gives a physical feel .
Plastic wrap (as a cover) - lay the plastic wrap loosely over the dish and press it to the sides. Vent plastic wrap by turning back one edge slightly to allow excess steam to escape. The dish should be deep enough so that the plastic wrap will not touch the food. Use plastic dishes, cups, semi-rigid freezer containers and plastic bags for short .
The plastic section modulus is used to calculate the moment capacity of a section when a plastic hinge has formed. Assuming perfectly plastic stresses, the balance of forces requires that the plastic neutral axis form at the half-area axis. The plastic section modulus is then the
intelligence until Deep Blue won the world championship from Kasparov—but even these researchers agree that something important is missing from modern AIs (e.g., Hofstadter 2006). While this subfield of Artificial Intelligence is only just coalescing, “Artificial General