C3 Coating: Solution for IC Testing (Reduction of Solder Migration)

Transcription

1 C3 Coating: Solution for IC Testing (Reduction of Solder Migration) Bert Brost Product Manager Valts Treibergs Engineering Manager R&D Nakany Katsura Kobelco Research Institut Inc. Abstract: Electronic components, such as ICs, LSIs, LEDs, are tested by contacting spring probe contactors to the electrode (pads). Good electrical characteristics (stable contact resistance), stable contact to the electrode (pads) of electrical components are required for such spring probe electrode (pads). Contact resistance of spring probe contactor is normally designed for low 100mΩ or less. However, contact resistance progressively gets worse from several hundreds of mill iohm to several ohm after repeated contact to solder pads. Because solder or pure-tin is very soft, it is scraped off at the time of contact, and easily sticks to the tip of spring probe. Also, because solder or pure-tin is easily oxidized resulting in high contact resistance, it is difficult to maintain stable contact during production IC testing. In addition to this, as contact counts increase, tip wear-out of the spring probe happens, resulting in unstable contact. To resolve the problems those mentioned above, periodical cleaning at the tip of contactors are being done, or frequent exchange of contactors are carried out. Also, various investigations, such as tip shape geometry, material design, and surface treatment of the tips are being carried out, however, no good solution exists to resolve problems mentioned above. As a result, because of lower first-pass testing yield, retest, and frequent cleaning, IC test cost increases. Diamond Like Carbon (DLC) has good characteristics: (a) DLC does not alloy with tin (), (b) has high durability (excellent hardness and wear characteristics), however, (c) specific resistance is high. Therefore, until now, DLC has been regarded not suitable for spring probe contacts. Kobelco Research Institute Inc. developed C3 Coating technology, which is surface treatment technology with conductive DLC. C3 Coating prevents from solder migration at the tip of contactors, also prevents wear-out of the tip of contacts, resulting in much more stable contact to electrode of electronic components. C3 Coating brings (a) long life of contactors, (b) improvement in first test pass yield and lowering retest rate, (c) less cleaning frequency and enhancing efficiency of IC testers, and contributing total test cost savings. Xcerra Corporation 825 University Avenue Norwood, MA T:

2 C3 Coating works extremely well with a robust material and unique probe tip design, such as Multitest s Quad Tech spring probe contacts. Multitest has applied its spring pin technology with C3 enhancement to achieve improved first pass yield, pin life, and reduced cleaning frequency. This presentation describes the coating technology and is illustrated by laboratory and customer case studies. Xcerra Corporation 825 University Avenue Norwood, MA T:

3 C3 Coating : Solution for IC Testing (Reduction of Solder Migration) Bert Brost, Valts Treibergs Xcerra Corporation Nakaya (Nick) Katsura Kobelco Research Institute Inc. Conference Ready mm/dd/ BiTS Workshop March 15-18, 2015 Presentation Agenda What is DLC and C3? In-house testing of C3 Cycle testing RF Testing Field evaluation results Matte QFN evaluation with Kelvin pin Production evaluation at ambient/hot Advantages of C3 C3 Coating : Solution for IC Testing 2

4 What is DLC (Diamond-Like Carbon)? Features of DLC High Hardness & Wear Resistance Low Coefficient of Friction Chemical Resistance Cutting Tools Shaver Typical Application of DLC Gas Barrier Biocompatibility Inner Wall of Plastic Bottles Stent (Medical) Features of DLC and Typical Applications (Source : Japan New Diamond Forum) C3 Coating : Solution for IC Testing 3 DLC Prevents Solder Migration Au Binary Phase Diagram of Au- Pd Binary Phase Diagram of Pd- Source : Binary Phase Diagrams, Thaddeus B. Massalsky The Materials Information Society C3 Coating : Solution for IC Testing 4

5 Development of C3 Coating (C3 Conductive Carbon Contact) C3 Film Conductive DLC Layer Adherent Layer C3 Coated Cross Section Of Plunger (Enlarge) Cross Section of Plunger C3 Coating : Solution for IC Testing 5 Contact Resistance (mω) Contact Resistance [mω] In-house Testing: Stable Contact to Pb- Free Solder 1,500 1, C3 Probe Conventional Probe (Au plated) Cycle Contact Count Count (thousands) ( x 1k ) Pb Free Solder Plate (Φ150mm) Contact Resistance (100k contacts w/o cleaning) - Pb-Free Solder : -3Ag-0.5Cu (SAC305) - Current : 100 ma, Data are plotted every 100 contacts - Full-Auto Wafer Prober is used - Temp: Ambient C3 Coating : Solution for IC Testing 6

6 In-house Testing: Stable Contact to Matte-Tin Contact Resistance (mω) Contact Resistance [mohm] Au Au probeprobe Pd-alloy probe - Pd Alloy Probe improved C3 probe - C3 Probe Cycle Contact Count Count (thousands) [x1k] C3 Coating : Solution for IC Testing Structure of Matte Tin Plate (8~10 µm) Cu base alloy Contact Resistance (500k contacts w/o cleaning) - Pb-Free Solder : Matte Tin Plate - Current : 100 ma, Data are plotted every 100 contacts - Full-Auto Wafer Prober is used - Temp: 85 C 7 Durability & Less Solder Migration Au Pd alloy C3 on Au Pin Top view SEM EDXmapp -ing 20 µm L 20 µm L Stuck Free Area 20 µm L Initial State of Pd Alloy Pin has Very Sharp Profile Side view SEM C3 Coating : Solution for IC Testing 8

7 Self-Cleaning Effect of C3 Coating 1 st. Contact : Tin Stuck to the tip (Temporarily) C3 Film Tin is stuck to the tip, very slightly and temporarily Tin from 1 st. contact Solder 2 nd. Contact and after : (Repeatedly) Solder Tested Solder Solder Solder Solder Self-Cleaning Effect (Tin is rejected from a contact region) Tin from 2 nd. contact C3 Coating : Solution for IC Testing 9 Reduction of Transfer (Why?) stuck Au plating stuck C3 film Au- Alloy Composiotion Rate [at%] Postion form boundary [ nm ] Au plating stuck Au plating Au boundary C3 film Inserted Figure : EDX result Cross sectional TEM & EDX 10 C3 Coating : Solution for IC Testing 10

8 Optimal Probe Geometry For C3 C3 probe Dual-Edge shape is optimal BGA Optimal probe shape to be D crown < D ball 0.5 Solder Ball Solder Ball D crown = D ball 0.7 D crown = D ball 0.5 C3 Coating : Solution for IC Testing 11 Geometry Probe of C3 Coating 250 Contact Resistance (mω) 抵 抗 値 (mω) C3 Probe No Problems normally Au Probe 実 効 的 接 触 面 積 の 逆 数 Inverse of Probe Contact Area C3 Coating : Solution for IC Testing 12

9 Smoothness of C3 Around Pin C3 Coating C3 Si wafer Roughness measured by AFM Surface Roughness roughness (Ra) highly smooth area angle ( ) C3 Coating : Solution for IC Testing 13 Suitable Shape for C3 Coating SEM Image (Enlarged) EDX Mapping (Tin) C3 on Au Plated Probe ( is less sharp) C3 on Pd Alloy Probe ( is much sharper) Pin Condtion after 100k Contacts to Pure Tin (85 ) C3 Coating : Solution for IC Testing 14

10 RF Performance Comparison Between C3 Coated and Gold Plated Pin C3 Coating : Solution for IC Testing 15 C3 Cleaning C3 is designed to be minimally cleaned Air blow-off is usually that all is needed Light plastic brush and thin SUS wire brush cleaning can be used Automated cleaning media: recommend to use soft sheets with fine abrasive particles: MIPOX SWE WA8000 ITS materials can also be used C3 Coating : Solution for IC Testing 16

11 Field Evaluation: C3 in Matte QFN Application Controlled lab application using virgin matte QFN packages very low current applied (1mA) Ambient pick and place test handler Standard MT GMK Kelvin test socket Cres measured through 2 probes and 2 DUT-Probe interfaces C3 Coating : Solution for IC Testing 17 Resistance change of pair (ohms) Baseline Cres of Gold Plated GMK040 (Pair) Cycle Count Pin-pair resistance quickly unstable in this test condition with customer devices C3 Coating : Solution for IC Testing 18

12 Cres of C3 GMK040 (Pair) Resistance change of pair (ohms) GMK040-C3(a) GMK040-C3(b) GMK040-C3( c) Cycle Count C3 Coating : Solution for IC Testing 19 Summary Comparison Au vs. C3 Resistance Change Pin-Pair (Ohms) GMK040( Au -run1) GMK040( Au - run 2) GMK040- C3(Run 1) GMK040- C3(Run 2) +1 sigma -1 sigma Average GMK040- C3( Run 3) +1 sigma sigma Average C3 Coating : Solution for IC Testing 20

13 Field Application #2 QFN Application RF Device - MT Gemini C3 Probe - MT9510 Handler- Hot/Ambient Test Yield % 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Uncoated Maximum Pin Life NO CLEANING Final yield First yield Yield gap CLEANING ENABLED 25% 20% 15% 10% 5% 0% Yield Gap 0K K C3 Coating : Solution for IC Testing 21 Functional Advantages of C3 Coating 1 Reduction of Migration - DLC does not form alloy with Tin (). Stable Contact to Solder 2 Hardness and Low Friction - DLC is a very hard material. - DLC is low-frictional material. High Durability Users Merits Total Cost Saving in IC Testing 1 Cost Savings in Testing Operations - Enhancement of Test Yield - Reduction of Re-Test Operation - Reduction of Maintenance / Longer MTBF (Less Cleaning) - Improvements of Tester Operation Ratio 2 Cost Saving of Probes - Longer Life of Probes C3 Coating : Solution for IC Testing 22