Navigating the Surface Finish Maze… Navigating the PCB Surface Finish Maze SMTA - Oregon Date: 18 May 2011 Darren Hitchcock Field Applications Engineer CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | Navigating the Surface Finish Maze… 2 Business Overview: Global Presence We are the only PCB Shop that has Global Footprint in 4 continents MINNESOTA GERMANY FPC Manufacturing ITO & Materials Manufacturing 325 K sq ft Headcount: 350 Rigid PCB Manufacturing 110 K sq ft Headcount: 450 CHINA - Zhuhai Rigid PCB Manufacturing FPC & Rigid Flex Manufacturing 1340 K Sq f Headcount: 9,100 CHINA - Shenzhen LCD Displays and Touch Sensor Manufacturing 291 K Sq ft BRAZIL Headcount: 2,900 Rigid PCB Manufacturing 100 K sq ft Headcount: 250 Electroless Nickel / Electroless Gold (ENEG) Direct Immersion Gold (DIG) CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | Over 13,000 people world wide, ~ 12,000 in China 3 A plating or coating applied to the exposed copper features of a Printed Wiring Board (PWB). Plating (metallic) Coating (metallic or organic) 4 How is the Surface Finish Applied? What is a Surface Finish? CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | Coating Plating (metallic) Surface OSP, HASL, Carbon etc. Electrolytic Electroless Immersion Horizontal Finish Equipment Metal Plating Note: (Base) Metal Plating is typically copper (in most cases). Horizontal or Vertical equipment Automated or Manual But for some Nickel or Nickel-Phosphorous serve as the solderable surface. Vertical CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 5 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 6 1 Why is a Surface Finish Required? Surface Finish Requirements • Coplanar (flat) The Surface Finish prepares and protects the conductors of a PWB for assembly, installation, and use. • Wire Bonding • Solderability (wetability) • In Circuit Test • Lead-Free (RoHS and WEEE compatible and compliant) • Compatibility with other Surface Finishes • Contact Resistance (Compression Connection) • Multiple Solder Cycles Daughter Card Edge Fingers Fuzz Button Pads Grounding Rails • Tarnish Resistance • Wear Resistance • Hardness • Chemical Resistance • Soldermask Plugging of Vias 7 Reflow, Wave, Rework • Multiple Component Types QFP, BGA, Passives, Press Fit, etc. • Cost • Reliability CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | Gold Aluminum Shock Vibration Thermal Cycling CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | Surface Finish Types 8 Surface Finish Types Most Common: •OSP (Organic Solderability Preservative) • ENIG (Electroless Nickel/Immersion Gold) • Imm Ag (Immersion Silver) Under Investigation: •ENEPIG (Electroless Nickel / Electroless Palladium / Immersion Gold) •ENIPIG (Electroless Nickel / Immersion Palladium / Immersion Gold) •Lead Free HASL •HP ENIG (High Phosphorous Electroless Nickel / Immersion Gold) •Direct Gold on Copper (Direct Immersion Gold, etc.) •Lead Free ENIG •I Ag / I Au (Immersion Silver / Immersion Gold) •Nanofinish • Imm Sn (Immersion Tin) •Sn-Pb HASL (Hot Air Solder Level) •Electrolytic Ni /Au (Electrolytic Nickel / Gold) •Hard Gold •Soft Gold •Flash Gold (thin, solderable – may be hard or soft) •ENEG (Electroless Nickel / Electroless Gold) •more common for packaging industry (chip carrier PWB) CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 9 Surface Finish Types CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 10 Electrolytic Plating • Electrolytic plating is achieved by passing an electric current through a solution (electrolyte) containing dissolved metal ions allowing the metal to deposit on the conductive surface of the PWB. Less Common •Carbon Ink (Screened on) •Electroless Nickel – Immersion Palladium •Selective Solder Strip (SSS) •Sn Ni (Tin-Nickel) •Unfused Tin-Lead •Reflow Tin-Lead • Electrolytic Plating requires: Anode Cathode Electrolyte Metal Ions • The PWB serves as the cathode and is connected to negative polarity of the rectifier • The Anode is connected to the positive polarity of the rectifier Multiple Surface Finishes •Hard Gold + Immersion Silver •Hard Gold + ENIG •Hard Gold + HASL •ENIG + OSP •??? • The metal ions in the plating bath are reduced at the conductive surface of the PWB building up the metal thickness • The Voltage, Amperage, Temperature, Time, and Purity of the solutions determine the properties and amount of the deposit. CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 11 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 12 2 Electrolytic Plating Electroless Plating • Process is Non-electrolytic and Non-galvanic Electrolytic Nickel-Gold (Depicted Below) - - + + + + P C B Then Solution Gold Solution Hydrogen is released by the reducing agent, oxidized, creating a negative charge at the surface. •A catalyst is normally deposited on the copper surface to facilitate further deposition. Titanium Nick el Nickel P C B No external electrons are needed (ie: no rectifier) • Electroless deposition uses chemical reducing agents to supply the electrons needed for metal deposition. •Process is Autocatalytic Deposit continues once the plating starts. •Examples: electroless nickel, electroless palladium, electroless gold, etc. Anode Cathode Anode Anode Cathode Anode •Uniform plating Electrolytic Gold Plating (Over Nickel) Electrolytic Nickel Plating CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | not prone to differences in circuit density • Generally harder and more brittle deposit than electroplated 13 Electroless Plating CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 14 Immersion Plating Electroless Nickel (Depicted Below) • Process is Non-electrolytic No external electrons are needed (ie: no rectifier) • Galvanic displacement reaction causes exchange of metal atoms on the surface with those in the solution. Ni ++ Nickel is dissolved and Gold replaces the nickel during ENIG process. •Examples: immersion palladium, immersion gold, etc. •For ENIG, the phosphorous co-deposited with the nickel is the reducing agent that allows for the immersion gold plating. •Uniform plating Ni not prone to differences in circuit density • More prone to localized galvanic etching of sacrificial metal Cu CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 15 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 16 Immersion Plating • Silver (Depicted Below) • Tin Cu ++ Galvanic Displacement - Simply an Exchange of Copper and Silver Atoms Ag ++ Pros & Cons of Each Surface Finish Cu Base Foil + Plated Copper CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 17 3 OSP (Organic Solderability Preservative) OSP Typical Equipment used for the Coating of OSP Conveyorized Horizontal OSP and Pre-Flux Line CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 19 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | ENIG (Electroless and Immersion Plating) Organic Surface Preservative - OSP Advantages • Flat, coplanar pads • Re-workable by PCB supplier • Cheap & simple process • Short and easy to control process • High reliability for SAC based solder joints • High temperature OSP’s are available • No additional investment over today Typical Equipment used for the Plating of ENIG Disadvantages • Limited heat cycle capability • • • 20 Newer developments better PCBA process control critical Having exposed Cu after PCBA In Circuit Test (ICT) is a concern • But also true today • In Circuit Test pins cut through organics leaving residues on test probes • Handling sensitive • Overall “tighter” process window for assembly provider Automated ENIG Plating Line (PAL) CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 21 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | Electroless Nickel Immersion Gold - ENIG Electroless Nickel Immersion Gold - ENIG Advantages CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 22 23 Disadvantages • Flat planar pads • Withstands multiple heat cycles • Expensive (gold) • Long shelf life • Process is difficult to control • Good solderability • Black pad potential • No exposed copper • High barrel reliability • Brittle Fracture for BGA type packages (under mechanical load) • Easy to use for ICT • Not handling sensitive • May not be suited for high speed signals (skin effect) • Adjustments necessary for Press Fit technology • Great concerns with reliability on SAC solders (mechanical load) CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 24 4 Immersion Silver Plating Immersion Silver or Immersion Tin Typical Equipment used for Horizontal Immersion Silver Plating Conveyorized Horizontal Immersion Silver Plating Line Smaller Proto Shops may use a CONFIDENTIAL Vertical Batch| Process Copyright ©2011 Multek. All rights reserved. | 25 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | Immersion Silver Advantages • Flat, coplanar pads • Consistent coating thickness • Withstands multiple heat cycles • Good shelf life Immersion Tin Disadvantages Advantages Adjustments necessary for press fit technology (high friction coefficient) • Flat, coplanar pads • Anti-tarnishing is critical to control • Very easy solder able • High reliability with Cu Sn IMC • Works well at ICT • Same metal as CuSnAg alloy (does not change alloy ratio much) • Well suited and proven for press fit technology • • Likes to build oxides Issues with process interruptions Likes to diffuse (and migrate) Best wet ability of all alternatives • • Easy to repair (PCBA) Potential issues with µvoids (“champagne” voids) • High solder joint reliability with Cu Sn inter-metallic • Very handling sensitive • Easy to probe at ICT • Not recommended for wear surfaces • Relatively simple process at PCB manufacturing • Creep Corrosion in high sulfur environments • Color and look • Fewer heat cycles possible than I Ag due to IM growth • 27 HASL (Hot Air Solder Level) Typical Equipment used for the Coating of HASL Relatively inexpensive • Rinsing is highly critical Likes to build oxides Diffuses into the copper • • • Grows inter-metallic (0.1µm/2 months) at RT and with every heat cycle Anti-tarnishing is critical to control • • Can be reworked CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | • • • • Disadvantages • • 26 Exposed Cu Color and look Fear of Sn Whiskers CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 28 Tin – Lead HASL Vertical and Horizontal HASL Equipment CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 29 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 30 5 Electrolytic Plating of Nickel and Gold Tin – Lead HASL Advantages Typical Equipment used for the Electrolytic Plating of Nickel and Gold Disadvantages • “Nothing Solders Like Solder” • Easily Applied • Lengthy Industry Experience • Easily Reworked • Multiple Thermal Excursions • Good Bond Strength • Good solder joint reliability • • • • Co-Planarity Difference • Inconsistent Coating Thickness • Contains Lead • Not Suited for High Aspect Ratios • Not Suited for fine-pitch SMT and Grid Array Packages Long Shelf Life • PWB Dimensional Stability Issues Easy Visual Inspection • Bridging Problems on Fine Pitch Cu/Sn Intermetallic (solder joint) • Subjects the PCB to High Temp • • Potential Off-Contact Paste Printing (on Varying Pad Sizes) CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | Automated Nickel and Gold Plating Line PAL and TAB Lines Shown 31 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | Electroplated Nickel / Gold Electroplated Nickel / Gold Disadvantages Advantages • Limitation is aspect ratio Very easy solder able • Limitation in line spacing at about 4-5 mil (100-125 µm) • Works well at ICT • Gold is expensive • Very high barrel reliability (PCB) • Recent great concerns with reliability • Very easy to rework (PCBA) • Flat, coplanar pads • • • • • Very long shelf life • Long and proven track record for high end products • Hard gold provides good wear surface • 10:1 max Lower joint strength using SAC alloys compared to OSP Inter-metallic phase fractures Sporadic in nature • CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 32 33 • Problem is not yet well understood Not so widely available in the industry CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 34 Lead – Free HASL Surface Finishes - 2012 Equipment being used for the Coating of Lead-Free HAL Same as for Leaded Versions but with a few Modifications • Higher Temp Steel Solder Pots and Stronger - Higher Temp Pumps • (Effective heat transfer by improved alloy circulation) Pre-heat panel (pre-dip) • Longer contact time with PCB • High temperature resistant chemistries (oils and fluxes) • Copper control (Drossing – Dilution and Skimming) • *Source: CEMCO / FSL CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 35 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 36 6 Lead – Free HASL Lead - Free HASL Disadvantages Advantages • Easily Applied and Reworked • Familiar HAL Dynamics • Good Bond Strength • Long Shelf Life • Easy Visual Inspection • CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | Wettability Subjects the PCB to VERY High Temperature • Copper Feature Dissolution • Co-Planarity Difference • Inconsistent Coating Thicknesses (on Varying Pad Sizes) • Not Suited for High Aspect Ratios • May not be suited for fine-pitch SMT and Grid Array Packages • PWB Dimensional Stability Issues • Bridging Problems on Fine Pitch • “Dull” and “Grainy” Appearance • More Process Controls Req’d Cu/Sn Solderjoint 37 Lead-Free Solder • Potential Off-Contact Paste Printing CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 38 LEAD-FREE HAL (Hot Air Level) Corrosion of Copper Pad The main considerations in changing a HAL process from 63/37 Sn/Pb to SN100C (Ni-stabilized Sn-0.7Cu) is: Original Pad 18µm Copper The higher melting point ALLOY MELTING PROCESS PROCESS POINT TEMPERATURE WINDOW 63/37 Sn/Pb 183°C 250°C(482) 67°C Sn-0.7Cu+Ni 227°C 265°C(509) 38°C *Source: Nihon Superior Co., LTD CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | After 6 Passes over Wave Soldering Machine 105°°C Preheat, 256°°C Solder Temperature, 4 seconds contact time 39 Sn-37Pb Sn-3.0Ag-0.5Cu CONFIDENTIAL Sn-0.7Cu+Ni | Copyright ©2011 Multek. All rights reserved. | Source: Florida CirTech, Inc. 40 ENEPIG Copper Dissolution Rate Alloy #1 Electroless Nickel / Electroless Palladium / Immersion Gold 40 sec contact 120 sec contact Alloy #2 15 sec contact • Boards were waved and reworked with 2 different alloys. Simulated mini-pot rework (no component removal) was performed from 0 – 120 second exposure. CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 41 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 42 7 ENEPIG • Electroless Nickel / Electroless Palladium / Immersion Gold ENEPIG • Advantages: E • Sometimes called the Universal Finish • Ni is 3-8 um thick (120 – 315 microinches) • Pd is 0.1 – 0.3 um thick (4 – 12 microinches) • Au is 0.02 – 0.05 um thick (0.8 – 2.0 microinches) CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 43 ENEPIG Gold and Aluminum Wirebonding Good Solderability No bussing bars needed to plate (not electrolytic) No concern with “Black Pad” because the Phosphorous is plated on the Electroless Nickel by chemical reduction, not galvanic like in ENIG, so there is no attack of the Electroless Nickel layer during ENEPIG. No excessive corrosion of the EP layer by the IG due to low phosphorus content of the EP layer and low thickness of the gold. Good surface wear resistance CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 44 ENIPIG Electroless Nickel / Immersion Palladium / Immersion Gold • Disadvantages: Less common in the industry doesn’t have the track record of the other finishes. So don’t know if there are no issue, or no issues…yet. • Further Investigation: Thin IMC layer – good or bad? High volume processing window – large or narrow? Surface finish cost? Immersion Gold is still galvanic with Electroless Phosphorous, are there any hidden issues with galvanic corrosion of the EP layer? CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 45 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 46 Direct Gold on Copper ENIPIG • Electroless Nickel / Immersion Palladium / Immersion Gold • Advantages: Gold and Aluminum wire bondable Good solderability (also in lead-free assembly) Palladium bath is less sensitive to impurities than with ENEPIG Faster processing time than ENEPIG Wider process window than ENEPIG Thinner Palladium deposit 0.3-0.5 um (1-2 microinches) Lower cost than ENEPIG I • Disadvantages: replacement / galvanic deposition of Palladium on the Electroless Nickel. Unknown issues with black pad type phenomenon however there is a very thin deposit of the palladium, so the corrosion attack should be minimized CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 47 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 48 8 Direct Gold on Copper Direct Gold on Copper • Gold is plated directly on the copper without a nickel barrier layer. • Advantages • Direct Immersion Gold Immersion Gold and Electroless Gold type deposition is used (not intuitive from DIG acronym) A mixed autocatalytic reaction and displacement reaction Uyemura study (>80% autocatalytic) – www.uyemura.com/library-3.htm Good for mixed surface finish PWB Multiple solder exposure during assembly Compatible with press fit connectors Good for flexible circuits Eliminate lossy nickel in high speed / RF applications Better coverage than standard immersion gold • Disadvantages Shelf Life – gold / copper migration concerns CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | Tight gold deposit is supposed to produce a non-porous deposit that resists copper migration into the gold. Slow deposition time High process bath temperature 49 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | High Phosphorous ENIG 50 HiPhos ENIG • Phosphorous >10% codeposited with the Electroless Nickel • Advantages Corrosion resistance Supposed to eliminate Black Pad risk Solderability and Reliability as good as Medium Phosphorous ENIG Drop-in to existing ENIG plating lines Lower internal stress in the Nickel deposit (better for flexible circuits) • Disadvantages CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | Not well known. Needs more testing Slower deposit rate than standard ENIG Nickel bath sometimes reacts with Sulfur content in some soldermasks 51 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 52 Lead Free ENIG Lead – Free ENIG • No Lead as a stabilizer in the Electroless Nickel bath The main reactions in the Electroless Nickel bath are the deposit of Nickel and Phosphor buildup of orthophosphite and other byproducts • Orthophosphite causes higher stress in nickel deposit which increases the risk of nickel corrosion • Other by products lead to breakdown of the soldermask which leads to sulphur buildup which increases the risk of nickel corrosion. • Heavy metals (Lead) and organic stabilizers are used to limit these buildups and corner attack. • Removal of Lead reduces corner attack, therefore a reduction in the amount of sulphur accelerator needed. This leads to an increase in corrosion resistance and a reduction in the associated risk of black pad. CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 53 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 54 9 ENAG ENAG Electroless Nickel / Immersion Gold / Electroless Gold • ENIG with additional Electroless Gold plated on top. • Used for thicker gold deposit • Advantages excellent for gold wirebonding (packaging, camera modules, etc.) reason for the thicker gold • Disadvantages CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | Not recommended for soldering – solder joint embrittlement risk due to amount of gold. 55 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | Immersion Silver / Immersion Gold 56 Imm Silver / Imm Gold • Immersion Silver deposit followed by Immersion Gold deposit Immersion Gold Immersion Silver • Currently under investigation Copper CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 57 PCB MATERIALS FINAL FINISH 2011 90 Electrolytic Ni/Au 12.0Mm 2 4% Reflowed Sn/Pb 1.5Mm 2 0.0% ImSn 2 14.6Mm 5% Electrolytic Ni/Au Reflowed Sn/Pb 8.5Mm 2 3.4% 1.9Mm 2 0.7% ImSn OSP 9.0Mm 2 3.6% 115.0Mm 2 46% 80 70 OSP 183.7Mm 2 58% Lf HASL 57.3Mm2 18% Lf HASL 46.0Mm 2 18% 58 2011 Surface Finish – select factories Final Finish Market Survey 2006 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 60 50 40 30 HASL 17.1Mm 2 5% 20 10 CAAGR 5.0% 0 ImAg 25.3Mm 2 8% HASL 52.1Mm 2 21% ImAg 10.4Mm2 4.2% Imm ENIG HASL Elec. Silver OSP Ni/Au ENIG 7.5Mm 2 2% ENIG 7.1Mm 2 2.8% TOTAL: 250Mm2 TOTAL: 319Mm2 Handheld MFF LFF Imm Tin ENIG + OSP Source: Prismark Partners CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 59 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 60 10 Conclusion Finish I Surface Finish Comparison There is no SINGLE perfect finish that “fits all” HASL (Sn-Pb) ENIG Imm Ag OSP Flatness poor good good good Solderability good good good fair Rework (Sn-Pb) good fair good good n/a fair good good Rework (Lead-free) Finishes should be selected based on specific product application (OEM-EMS key) US market tends to favor I Ag (larger and thicker boards) EU tends to favor I Sn (smaller and thinner boards) Handhelds prefer OSP/ENIG OSP is used in all product application areas All other finishes will be niche (currently) acceptable in some good - button, good - ICT, applications poor - wiping poor - wear poor No Yes Yes Yes oxidizes yes fair fair Solder Joint Reliability (thermal cycle) good fair good good Solder Joint Reliability (shock) good poor good good low high low low Contact Resistance (Wear) RoHS (compliant) Tarnish Resistance Cost CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 61 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 62 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 63 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 64 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 65 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 66 Thank You Thank You 11 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 67 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 69 CONFIDENTIAL | Copyright ©2011 Multek. All rights reserved. | 68 12