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Application Note: Packaging
Implementation Solder Reflow Guidelines Pb-Free Packages
Author:
XAPP427 (v2.4) February 2009
Summary
Recent legislative directives corporate driven initiatives around world have called elimination other hazardous substances electronics used many sectors electronics industry. Pb-free program Xilinx established 1999 proactive effort develop qualify suitable material sets processes Pb-free applications. Xilinx taken leadership position quickly forming partnerships with customers, suppliers, participating industry consortiums provide technical solutions that aligned with industry requirements. Xilinx researched alternatives compounds selected matte lead finish lead-frame packages SnAgCu solder balls packages. addition, suitable material sets have been chosen qualified higher reflow temperatures (245°C-260°C) that required Pb-free soldering processes. Pb-free products from Xilinx designated with additional package designator portion part number. reflow soldering applications, SnAgCu solder been chosen industry most viable Pb-free solder replace eutectic Sn/Pb solder. Compared with other Pb-free alloys, SnAgCu better characteristics terms cost processability well comparable better reliability than eutectic Sn/Pb solder. However, SnAgCu alloy much higher melting temperature (217°C) than standard eutectic Sn/Pb solder. Thus, assembly processes must optimized accordingly achieve best yields reliability. This document contains guidelines reflow soldering, inspection, rework process Pb-free packages.
Backward Compatibility
Backward compatibility, described this Application Note, refers only soldering process. Pb-free devices from Xilinx have same form, function standard Pb-based products. changes required board design when using Pb-free products from Xilinx. However, finish materials boards might need adjusted. Xilinx® standard packages recommended Pb-free process. Lead-frame packages (PQG, TQG, VQG, PCG, etc.) from Xilinx backward compatible, meaning that component soldered with Sn/Pb solder using Sn/Pb soldering process. Lead-frame packages from Xilinx matte plating leads, which compatible with both Pb-free soldering alloys Sn/Pb soldering alloy. packages (CPG, FTG, FGG, BGG, etc.), however, recommended soldered with Sn/Pb solder using Sn/Pb soldering process. traditional Sn/Pb soldering process usually peak reflow temperature 205°C-220°C. this temperature range, SnAgCu solder balls properly melt soldering surfaces. result, reliability assembly yields compromised. Special considerations Pb-free soldering shown Reflow Soldering Considerations section.
2002-2009 Xilinx, Inc. XILINX, Xilinx logo, Virtex, Spartan, ISE, other designated brands included herein trademarks Xilinx United States other countries. other trademarks property their respective owners.
XAPP427 (v2.4) February 2009
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Reflow Soldering Considerations
Reflow Soldering Considerations
reflow soldering process Pb-free components very similar conventional eutectic solder reflow process. However, there some important differences that must taken into consideration Pb-free soldering soldering material used Pb-free soldering different higher reflow temperatures required. optimal profile must take into account solder paste/flux used, size board, density components board, between large components smaller, lighter components. Profiles should established board designs using thermocouples multiple locations component. addition, there mixture devices board, then profile should checked various locations board. Ensure that minimum reflow temperature reached reflow larger components same time, temperature does exceed threshold temperature that might damage smaller, heat sensitive components. general, gradual, linear ramp into spike been shown various sources optimal reflow profile Pb-free solders (Figure This profile been shown yield better wetting less thermal shock than conventional ramp-soak-spike profile Sn/Pb system. SnAgCu alloy reaches full liquidus temperature 235°C. When profiling, identify possible locations coldest solder joints ensure that those solder joints reach minimum peak temperature 235°C least seconds. might necessary ramp peak temperature 260°C above. Reflowing high peak temperature 260°C above damage heat sensitive components cause board warp. Users should reference latest JEDEC J-STD-020 standard allowable peak temperature component body. allowable peak temperature component body dependent size component. Refer Table peak package reflow body temperature information. case, reflow profile with lowest peak temperature possible should used. sophisticated boards with substantial large small components, critical minimize delta across board (less than 10°C) minimize board warpage thus, attain higher assembly yields. Minimizing delta accomplished using slower rate warm-up preheating stages. heating rate less than 1°C/sec during preheating soaking stages, combination with heating rate more than 3°C/sec throughout rest profile highly recommended. also important minimize temperature gradient component, between surface bottom side, especially during cooling down phase. fact, cooling crucial part reflow process must optimized accordingly. While slow cooling rate result high assembly yields, could lead formation thick intermetallic layers with large grain size; thereby, reducing solder joint strength. other hand, faster cooling rate leads smaller solder joint grain size, results higher solder joint fatigue resistance. However, overly aggressive cooling stiff packages with large thermal mass lead cracking package warpage because differential cooling effects between surface bottom side component between component materials. optimize cooling with minimal temperature differential between surface package solder joint area. temperature differential between surface component solder balls should maintained less than during critical region cooling phase reflow process. This critical region phase which balls completely solidified board yet, usually between 200°C-217°C range. best solution might divide cooling section into multiple zones, with each zone operating different temperatures efficiently cool parts. Table Figure provide guidelines profiling Pb-free solder reflow.
XAPP427 (v2.4) February 2009
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Reflow Soldering Considerations
Table Pb-Free Reflow Soldering Guidelines
Profile Feature Ramp-up rate Preheat Temperature 150°-200°C Temperature maintained above 217°C Time within actual peak temperature Peak Temperature (lead/ball)
Convection, IR/Convection
3°C/second 60-120 seconds 60-150 seconds (60-90 seconds typical) seconds 235°C min., 245°C typical (depends solder paste, board size, components mixture) 245°C-260°C, package body size dependent (reference Table 6°C/second minutes min, minutes typical, minutes
Peak Temperature (body) Ramp-down Rate Time 25°C Peak Temperature
X-Ref Target Figure
Tbody (max) 245-260°C (package type dependent) Table value each package Tlead (min) 235-260°C (10s minimum) Ramp down 6°C/s
Temperature (°C)
217°C Wetting time 60-150 150-200°C Ramp 3°C/s Preheating 60-120s
Time
X427_01_020609
Figure
Typical Conditions Pb-Free Reflow Soldering
Table Peak Package Reflow Body Temperature Xilinx Pb-Free Packages (Based J-STD-020 Standard)
Package Peak Package Reflow Body Temperature Lead Frame PCG20 PCG44 PCG68 PCG84 PDG8 PQG100 PQG160 PQG208 PQG240 JEDEC Moisture Sensitivity Level (MSL)
PLCC
245°C
Plastic
250°C
PQFP
245°C
XAPP427 (v2.4) February 2009
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Reflow Soldering Considerations Table Peak Package Reflow Body Temperature Xilinx Pb-Free Packages (Based J-STD-020 Standard) (Cont'd)
Package PQFP (Heatsink) HQG208 HQG240 HQG304 TQG100 TQG128 TQG144 VQG44 VQG64 VQG100 VOG8 VOG20 VOG48 SOG20 Peak Package Reflow Body Temperature 245°C JEDEC Moisture Sensitivity Level (MSL)
TQFP
260°C
VQFP
260°C
VO/SO
260°C
BGA/FlipChip FTG64 FTG256 FGG256 FGG320 BGG225, BGG256 BGG575 FGG324 FGG400 FGG456 FGG484 FGG556 FGG676 FGG900 BGG728 FGG1156 BGG352 BGG432 BGG560 FGG680 FGG860 CPG56 CPG132 CSG48 CSG144 CSG280 CSG484 FSG48
260°C
(Cavity
250°C
245°C
(Cavity Down)
260°C
245°C
Chip Scale
260°C
XAPP427 (v2.4) February 2009
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Reflow Oven Table Peak Package Reflow Body Temperature Xilinx Pb-Free Packages (Based J-STD-020 Standard) (Cont'd)
Package SFG363 FFG323 FFG324 FFG665 FFG668 FFG672 FFG676 BFG957 FFG896 FFG1136 FFG1148 FFG1152 FFG1153 FFG1513 FFG1517 FFG1696 FFG1704 FFG1738 FFG1759 FFG1760 QFG32 QFG48 Peak Package Reflow Body Temperature 260°C JEDEC Moisture Sensitivity Level (MSL)
250°
Flip Chip
245°C
260°C
Reflow Oven
achieve consistently high assembly yields, upgrade newer equipment with more zones might necessary have better process control (minimizing delta forced convection reflow oven recommended while reflow might suitable.
Nitrogen
Although nitrogen required, recommended achieve better wettability widen process window. Nitrogen especially beneficial when temperature differential across board large. Additionally, nitrogen improves appearance solder joints inhibiting effects oxidation.
Inspection
Pb-free solder joint looks duller grainier than Sn/Pb solder joints. This mainly surface roughness high Pb-free solder alloy. Additionally, wetting spread generally great with Sn/Pb solder joints. Training must provided technicians/operators distinguish Pb-free solder joints from Sn/Pb solder joints. More detailed information found latest IPC-A-610D Standard [Ref
Hand Soldering
important factors hand soldering quality soldering iron skill technician. Tight temperature time control especially critical Pb-free applications higher temperature. Excessive soldering iron temperature result dewetting thermal damage boards components. When temperature high enough, when flux activation insufficient, poor wetting occur. Using correct solder temperature with adequate heat transfer essential creating reliable solder joints [Ref Preheating recommended reduce delta avoid having higher operating temperature. temperature duration depends size joint. general, temperature higher than Sn/Pb soldering range 350°C-375°C duration seconds. might necessary some cases different solder sized tips best result. Larger tips more suitable larger joints. There soldering systems available market today that allow variable power, constant temperature regardless load. Constant temperature important
XAPP427 (v2.4) February 2009
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Pb-Free Rework Pb-free soldering since reduces operator intervention eliminates risk causing thermal damage delicate components.
Finally, critical maintain clean since Pb-free more sensitive dirty soldering iron tips.
Pb-Free Rework
successful rework minimize temperature difference between solder joint component body. When setting profile, place thermocouples following locations: package, bottom center solder joint, corner areas solder joint. achieve good wetting, peak temperature 230° C-235° minimum solder joint necessary. Additionally, time above liquidus (217° should 45-90 seconds range. minimize temperature differential between solder joint component body, adequate bottom side heating board recommended. Before engaging nozzle, users should apply bottomside heat until board reaches 150° nozzle should optimized that heat goes mainly solder joint areas. addition, important ensure that component body temperature does exceed allowable limit (245°C-260°C, package size dependent, Table Allowable maximum component body temperature dependent package size volume. This information found latest J-STD-020 standard.
More Information
Reliability information Pb-free products available Device Reliability Report which found Xilinx site more information about Pb-free products from Xilinx, visit Pb-free site www.xilinx.com/pbfree.
References
IPC-A-610D "Acceptability Electronic Assemblies", Association Connecting Electronics Industries, February 2005. Bath, Jasbir al., "Lead-Free Soldering", Springer-Verlag, 2007. American Competitive Institute, "Initiatives Lead Free Soldering," www.aciusa.org. Bath, Jasbir, Handerwer, Carol, Bradley, Edwin, "Research Update: Lead-Free Solder Alternatives," www.circuitassembly.com, 2000. Gilleo, Ken, Area Array Packaging Handbook, copyrighted 2002 McGraw-Hill Co., pages 14.14-14.16. Hall, James, "Concentrating Reflow's Cooling Zones," EP&P, 3/01/2001 Narrow, Phil, "Soldering," Magazine, August 2000 Parker, Richard, "The Next No-Lead Hurdle: Components Supply Chain," www.circuitree.com, August 2000. Peo, Mark, DeAngelo, Don, "New Reflow Profiles Oven Configurations Must Explored Meet Needs Lead-Free Solder Paste," www.smtmag.com, 2000. Selig, Karl Suraski, David, Practical Guide Achieving Lead Free Electronics Assembly," www.aimsolder.com.
XAPP427 (v2.4) February 2009
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Revision History
Revision History
following table shows revision history this document.
Date 12/09/02 09/16/04 12/09/05
Version Initial Xilinx release.
Revision
General revision conform revised Pb-free document standards. Ramp-up rate data Table Figure revised. Peak reflow temps revised, added packages, changed flip chip lead free designations from Table Table updated include VOG8 value. Table updated include CSG484,FFG323, FFG324 FFG1738 information, removed +0/-5°C tolerance from peak temperatures. Added [Ref [Ref Added more information Inspection, page Hand Soldering, page Table updated include FTG64, FFG665, FFG1136, FFG1153, FFG1759. Revised Table page Figure latest JEDEC standards.
01/30/06 11/17/08
02/12/09
Notice Disclaimer
Xilinx disclosing this Application Note "AS-IS" with warranty kind. This Application Note possible implementation this feature, application, standard, subject change without further notice from Xilinx. responsible obtaining rights require connection with your implementation this Application Note. XILINX MAKES REPRESENTATIONS WARRANTIES, WHETHER EXPRESS IMPLIED, STATUTORY OTHERWISE, INCLUDING, WITHOUT LIMITATION, IMPLIED WARRANTIES MERCHANTABILITY, NONINFRINGEMENT, FITNESS PARTICULAR PURPOSE. EVENT WILL XILINX LIABLE LOSS DATA, LOST PROFITS, SPECIAL, INCIDENTAL, CONSEQUENTIAL, INDIRECT DAMAGES ARISING FROM YOUR THIS APPLICATION NOTE.
XAPP427 (v2.4) February 2009
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