IMPROVING RF POWER TRANSISTOR RELIABILITY WITH NEW PLASTIC PACKAGES. Laurent GAUTHIER RF FAE Toulouse, France

Transcription

1 IMPROVING RF POWER TRANSISTOR RELIABILITY WITH NEW PLASTIC PACKAGES Laurent GAUTHIER RF FAE Toulouse, France 0

2 Plastic Devices for all RF Markets 1

3 Power Freescale Plastic Package Evolution 1000W TO270WBL4 OM W TO272WB16 TO270WB4 TO272WB4 OM780 OM880 TO270WB14 TO270 TO272 PQFN 10W SOT89 PFP16 PLD

4 Why a new Plastic Package? 3

5 Top benefits of OMNI over ceramic packages Lower thermal resistance, enabling smaller heatsink or better reliability Tighter dimensional tolerance, enabling assembly automation Same thermal expansion (copper on copper), enabling better reliability (no mismatch at solder joint) More power in smaller and lighter package 600 W 1250 W 4 Leveraging two decades of leadership in plastic packaging in the cellular infrastructure market, Freescale is now bringing the benefits of plastic packages to industrial applications

6 From Air Cavity to Over Molded packages AIR CAVITY : NIxxxx oceramic window frame and ceramic lid, attached with epoxy oau plating on heatsink and leads oau wire bond omulti die capability oausi eutectic die attach ocu laminate heatsink OVER MOLDED : TOxxxx o Epoxy mold compound surrounds the die and wire bonds o Sn plating on Cu heatsink and leads o Al wire bond o Single die capability o Soft solder die attach o Cu heatsink OVER MOLDED : OMxxxx o Epoxy mold compound surrounds the die and wire bonds o Sn plating on Cu heatsink and leads o Al wire bond o Multi die capability o AuSi eutectic die attach o Cu heatsink 5

7 OM packages superior performances Over molded package (OM vs NI): Reduce dimensional tolerance (0.003 vs ) Reduce bonding wire temperature 225 C Tj capable Eliminate bonding wire vibration Reduce weight Cu flange (OM vs NI): Reduce thermal resistance (CU : 400W/m-K vs Cu lam : 250 W/m-K) Multi die capabilities (OM vs TO) : Increase function integration AuSi Eutectic die attach (OM vs TO) : Lower thermal resistance Increase the solder joint reliability with less CTE mismatch (Coefficient of Thermal Expansion. Should be harmonized for solder and flange to withstand soldering processes involved during manufacture and the temperature cycles that occur during operation.) 6

8 Comparing MRFE6VP61K25N / H Thermal Resistance MRFE6VP61K25H bolted MRFE6VP61K25N soldered 7

9 OM1230 vs NI1230 (Soldered) FM Amplifier : Pout : 1250W Eff : 80% Pin=1563W Pout=1250W DT=12 C Plastic Ceramic Tjunction=79 C Tjunction=91 C Rjc=0.06 C/W Rjc=0.10 C/W Pdiss=313W Theatsink=60 C 8

10 OM1230 : Soldered vs Clamped FM Amplifier : Pout : 1250W Eff : 80% Pin=1563W Pout=1250W DT=28 C Nota : greater difference will be found between screwed NI1230 and soldered OM1230 Soldered Clamped Tjunction=79 C Tjunction=107 C Rjc=0.06 C/W Rjc=0.15 C/W Pdiss=313W Theatsink=60 C 9

11 Thermal Performances Confirmed MRF8S7120N, Cu Laminate MRF8S9120N, Pure Cu Pdiss : 70W Tc : 80 C Tj: 133 C Rjc: 0.75 C/W 15% Rjc improvment Pdiss : 76W Tc : 80 C Tj: 126 C Rjc: 0.65 C/W and up to 30% Rjc improvement on MRFE6VP61K25N! 10

12 Impact of Junction Temperature on MTTF DT=9 C : MTTF divided by 3 DT=28 C : MTTF divided by 16 or Replacing a screwed NI1230 by a soldered OM1230 device will increase MTTF by a ratio of 16. In some case, that may cancel the need to have removable parts. MRFE6VP61K25HS 11

13 Dimensional tolerances Example: width tolerances Freescale: +/- 5mils Competitors: +/- 20mils Benefits: ease of use in manufacturing Ready for machine automation in manufacturing Length Width 12

14 All plastics absorb and retain some moisture. During solder reflow assembly operation, the moisture inside the package can induce stress, potentially leading to failures. MSL levels: MSL 6 Mandatory Bake before use MSL 5A 24 hours MSL 5 48 hours MSL 4 72 hours MSL hours (1 week) MSL 2A 4 weeks MSL 2 1 year MSL 1 Unlimited Susceptibility of packaged device to moisture-induced stress is properly measured and classified under MSL rating, established by Standards Organizations: IPC, JEDEC under EIA. (JEDEC Standard J-STD-20B) MSL classifications of a part when properly followed (packaging for shipment, storing, and handling) avoids any thermo-mechanical damage during assembly, solder reflow and repair operation. Freescale Plastic Packages are MSL 3 rated at 260 C reflow capable 13

15 Plastic Packages Qualification 14

16 High Reliability Today for Plastic Packages Plastic packaging has been the dominant semiconductor packaging technology for the last 40 years. Since the 1970 s, the improvements made in plastic compounds and manufacturing technology has resulted in decrease in defectivity of over molded plastic packages by two orders of magnitude. Freescale s RF Power plastic packages follow technology used for many years in high power low frequency packages (e.g. TO220 etc.) Several industry standards committees have established practices for qualification and reliability testing of plastic packages Freescale follows a complete set of industry standard testing practices for RF Power Plastic Packages including preconditioning for MSL (Moisture Sensitivity Level) ratings and for Pb free processing. In the last 15 years, Freescale has shipped ~180 million RF Power Plastic devices with no field returns due to package induced failures. 15

17 Package Qualification Requirements Various Reliability stress tests are imposed as part of product qualification. Not all of the tests are performed on every Product Technology. Tests are based on die and package technology reuse. Metal- Discrete Plastic IC Purpose Ceramic Plastic Temp Cycling TC x + PreCond + PreCond Accelerates the effects of thermal expansion mismatch High Temp/Humidity TH x Test the moisture and corrosion resistance High Temp/Humidity with Bias THB + Precond* + Precond* Test the moisture and corrosion resistance High Temp Operating Life HTOL x or SSOL or SSOL Electrical stress under accelerated temperature Intermittent Operating Life IOL x Ability of the device to withstand intermittent Operation Steady State Operating Life SSOL or HTOL or HTOL Electrical stress under accelerated temperature High Temp Reverse Bias HTRB x x Test intrinsic transistor stability High Temp Gate Bias HTGB x x Test integrity of the gate oxide High Temp Storage Life HTSL x x x Package degradation due to high temperature storage (*) On the third reflow exposure, the parts could be soldered to a PCB if required. Pre-conditioning is based on the MSL rating of the device 16

18 Continuous Monitoring of Product Reliability Freescale uses Reliability Audit Program (RAP) to monitor the product quality. Each quarter, some of the higher running parts that are being produced on each key package platform are selected for RAP monitoring. Samples are randomly selected and put through series of key reliability tests to assure that the product reliability is not being affected. 17

19 RF Devices Mounting Methods 18

20 Preliminary comments Discussed items on device mounting should be seen as general guidelines. It may not be applicable to all situations. Every part of the design (solder, material, surface finish, size ) should be study and defined according to maker s experience, process used and quantities. 19

21 Plastic OM-1230 mounting methods 20

22 Soldering OM L package OM1230-4L device Solder PCB Copper Carrier Solder Thermal interface Aluminium Heatsink Sequence of operation : Pcb soldered or screwed on copper carrier Device inserted under pressure Heating of carrier+pcb+device to solder device on carrier and pcb 21

23 Soldering OM-1230-G-4L package (1) NI S Gull device Solder PCB Copper Carrier Solder Aluminium Heatsink Copper carrier is inserted during pcb building Sequence of operation : Pcb soldered or screwed on copper carrier Device inserted under pressure Heating of carrier+pcb+device to solder device on carrier and pcb 22

24 Soldering OM-1230-G-4L package (2) NI S Gull device Solder PCB Metal Coin or Pallet Solder Aluminium Heatsink Metal coin is inserted during pcb building Sequence of operation : Pcb soldered or screwed on metal coin Device inserted under pressure Heating of coin+pcb+device to solder device on coin and pcb 23

25 Material and Finishes 24

26 PCB Possible pcb finishes : o NiAu o OSP (Organic Solderability Preservation) : low cost, easy handling, environmental friendly o Immersion Sn 25

27 Heatsink interface Surface finishes : o Flatness : 0.01mm o Ra < 0.5µm o No burrs Optionnal plating (ROHS) : o Dependant of process o Chrome 3 plating (electroplating) o Chromate conversion coatings (Iridine, Alodine, Surtec ) (passivation) Thermal interface o Small prod / lab eval : 50µm Thermal grease (such as HTCX grease from Electrolub) o Bigger prod : thermal preform possible (metal foils like copper, pads with graphite) 26

28 Solder Pb free solder paste / preform : o Commonly used SAC (Sn/Ag/Cu : Ag : 3-4%, Cu : 0-1%) provides near eutectic solder o Melting temperature around 217 C o Reflow temperature >235 C Solder paste thickness : 150µm Solder inspection: o Visual inspection : wetting appearance, visual appreance (dull for pb free) o Voids level (X-Ray/CSAM control) <25% min(association Connecting Electronic Industry) <10% : very good o Cross section Solder should not touch package body (NI-1230) or exceed carrier top level 27

29 Copper Carrier/Coin Surface finished : Flatness : <0.01mm Roughness : <0.5µm No burrs Optionnal plating : Process dependant Electroless nickel immersion gold (ENIG) may be used, it offers excellent surface planarity (also used for PCBs with large BGA packages) and good oxidation resistance 28

30 Sizing copper carrier Carrier is normally made of copper alloys Thickness (t) and extension (d) affect thermal resistance Recommandations : T>3mm D>5.5mm AN 1907 provides additionnal information 29

31 Copper carrier additionnal requirements Carrier can also help cooling matching components. Additionnal extension (d) is then needed. Screws are used to position pcb on carrier before soldering. They also help for electrical continuity. Channels are used to evacuate solder flux and excess thermal grease 30

32 Available Application Notes AN1907 : Solder Reflow Attach Method for High Power RF devices in Over- Molded Plastic Pakages : Carrier design considerations Geometrical sizing PCB layout considerations PCB to carrier attach Solder material PCB assembly process and reliability AN1908 :Solder Reflow Attach Method for High Power RF Devices in Air Cavity Packages Same as AN1907 but for Air Cavity packages RFPLASTICWP : Designing with Plastic Power Transistors : Mounting options, heat removal, smd or not, gull wing or straight leads, via farm design, reliability AN3789 : Clamping of High Power RF Transistors and RFICs in Over-Molded Plastic Packages : Design of clamp, impact on performances 31

33 Key Points Plastic package has demonstrated comparable reliability to ceramic package (180Millions devices produced those last 15 years at Freescale). New Plastic package allow better thermal performances : Lower die temperature Better reliability with increased MTTF The full benefit of better thermal performances is gained by soldering the plastic package to the copper carrier. Increased mechanical accuracy allows full automation of the pcb assembly and soldering process. 32

34 Freescale Semiconductor, Inc. Confidential and Proprietary