Cracking Problems and Mechanical Characteristics of PME and BME - PowerPoint PPT Presentation

NASA Electronic Parts and Packaging (NEPP) Program Cracking Problems and Mechanical Characteristics of PME and BME Ceramic Capacitors Alexander Teverovsky AS&D, Inc. Work performed for Parts, Packaging, and Assembly Technologies Office, NASA GSFC, Code 562 Alexander.A.Teverovsky@nasa.gov Presented by Alexander Teverovsky at the 2018 CMSE Components for Military & Space Electronics Training & Exhibition, Los Angeles, CA, May 7-10, 2018.

List of Acronyms BME base metal electrode IFT Indentation Fracture Test C-SAM C-mode scanning acoustic IR insulation resistance microscopy direct current leakage IWT ice water test DCL DF dissipation factor MLCC multilayer ceramic capacitor ECM electrochemical migration MOR modulus of rupture energy dispersive EDS PME precious metal electrode spectroscopy EM electrical measurements RH relative humidity ESR Equivalent series resistance TSD terminal solder dip FA failure analysis VH Vickers hardness Presented by Alexander Teverovsky at the 2018 CMSE Components for Military & Space Electronics Training & 2 Exhibition, Los Angeles, CA, May 7-10, 2018.

Abstract Most failures in MLCCs are caused by cracking that create shorts between opposite electrodes of the parts. A use of manual soldering makes this problem especially serious for space industry. Experience shows that different lots of ceramic capacitors might have different susceptibility to cracking under manual soldering conditions. This simulates a search of techniques that would allow revealing capacitors that are most robust to soldering-induced stresses. Currently, base metal electrode (BME) capacitors are introduced to high-reliability applications as a replacement of precious metal electrode (PME) parts. Understanding the difference in the susceptibility to cracking between PME and BME capacitors would facilitate this process. This presentation gives a review of mechanical characteristics measured in-situ on MLCCs that includes flexural strength, Vickers hardness, indentation fracture toughness, and the board flex testing and compare characteristics of BME and PME capacitors. A history case related to cracking in PME capacitors that caused flight system malfunctions and mechanisms of failure are considered. Possible qualification tests that would allow evaluation of the resistance of MLCCs to manual soldering are suggested and perspectives related to introduction of BME capacitors discussed. Presented by Alexander Teverovsky at the 2018 CMSE Components for Military & Space Electronics Training & 3 Exhibition, Los Angeles, CA, May 7-10, 2018.

Outline  Problems with cracking of MLCCs.  In-situ mechanical testing.  Flexural strength.  Vickers hardness.  Indentation fracture toughness.  Board flex testing.  Failure history case.  What can be done to mitigate manual soldering cracking.  Conclusion. Presented by Alexander Teverovsky at the 2018 CMSE Components for Military & Space Electronics Training & 4 Exhibition, Los Angeles, CA, May 7-10, 2018.

Cracking-Related Problems  Mechanism of cracking during manual soldering.  Revealing cracks in capacitors (loose and soldered).  Electrical measurements (C, DF, IR, VBR)  Electromechanical effects  Visual, radiography, ultrasonic analysis  Effects of cracking on reliability in humid and HT environments.  Robustness of MLCCs towards thermo-mechanical stresses.  IWT (ice water testing) Degradation of MLCCs with  TSD (terminal solder dip testing) cracks and the effectiveness of  In-situ mechanical testing. different techniques is described  Flexural strength in various publications and reports  Vickers hardness posted at the NEPP web site.  Indentation Fracture Test  Board flex testing  Susceptibility to cracking of PME and BME capacitors.  Do different types of MLCCs have different susceptibility to cracking under manual soldering conditions and how it can be revealed? Presented by Alexander Teverovsky at the 2018 CMSE Components for Military & Space Electronics Training & 5 Exhibition, Los Angeles, CA, May 7-10, 2018.

Flexural Strength  The test is described in AEC-Q200, but acceptance criteria are up to the users. AEC-Q200-003 600 Effect of case size on MOR C D R 3 5 B X 1 0 4 A K U S , 0 .1 u F , 5 0 V , s iz e 1 8 2 5 , M fr.C 9 9 500 1 0 N 9 0 5 N characteristic MOR, MPa PME 2 .5 N 400 BME 5 0 cumulative probability, % Modulus of 300 rupture 4 5 200 8 7 1 0 3 FL 4 100 MOR = 3 7 in itia l 5 19 8 13 a c tiv a te d ro s in flu x p o lis h e d 2 0 m o is tu re : 1 6 0 h r, 8 5 % R H , 2 2 C 2 bd m o is tu re : 1 6 0 h r, 8 5 % R H , 2 2 C T S D 3 5 0 & m o is tu re 1206 1210 1808 1812 1825 2225 1 case size 4 0 1 0 0 4 0 0 M O R , M P a  No effect of possible flaws but surface cracks reduce MOR.  Smaller size MLCCs have greater strength – Benefits of BMEs.  No substantial difference between BME and PME capacitors.  Variations of MOR values from lot to lot might exceed 50%.  The test can be used for relatively large (≥1206) parts.  Same size capacitors can be used for comparative analysis. Presented by Alexander Teverovsky at the 2018 CMSE Components for Military & Space Electronics Training & 6 Exhibition, Los Angeles, CA, May 7-10, 2018.

Vickers Hardness  Hardness is a resistance to indentation.  Testing is specified in ASTM C1327-15 (2015) V ic k e rs H a rd n e s s T e s t fo r P M E a n d B M E C a p a c ito rs 9 9 Vickers test, LT capacitors 700 600 500 BME y = 191.65x × cumulative probability, % 1 . 854 P = D^2, um^2 400 VH PME 2 SN1 5 0 300 D SN2 200 SN3 SN4 100 1 0 SN5 90% confidence 5 0 0 1 2 3 4 1 load, N 7 8 9 1 0 1 1 1 2 V H , G P a  In-situ VH measurements are possible using MLCCs with relatively thick cover plates. P should be low so the depth of the indentation is < 2x the thickness of the cover plate.  No correlation between strength and VH for ceramic materials.  No significant difference between PME and BME capacitors.  Reduction of errors might allow for revealing differences in lots. Presented by Alexander Teverovsky at the 2018 CMSE Components for Military & Space Electronics Training & 7 Exhibition, Los Angeles, CA, May 7-10, 2018.

Indentation Fracture Test  Fracture Toughness: the ability of a material to withstand stresses in the presence of cracks.  IFT technique is the most controversial. 0 . 5 180     PME_L capacitors E P Different lots of capacitors 1.60 = ξ     160 IFT 1.35 1.33 1.40 R _ M     1 . 5 VH c 140 1.20 Kc, Mpa_m^0.5 1.07 1.03 1.00 c^1.5, (um)^1.5 120 1.00 0.89 0.83 100 0.80 PME PME BME 0.60 L1 80 BX BP X7R PME_L1, 1.7 0.40 L2 60 PME-L2, 1.32 0.20 L3 40 IFT avr 1.08 1.46 0.95 0.00 PME_L3, 1.49 20 PME_L4, 1.20 STD 0.20 0.19 0.23 0 0 1 2 3 4 5 N 12 2 6 load, N  Test results depend on environments and time of exposure.  IFT might be useful for selecting parts for manual soldering, but more work is necessary to reduce errors and select criteria.  No significant difference between PME and BME capacitors. Presented by Alexander Teverovsky at the 2018 CMSE Components for Military & Space Electronics Training & 8 Exhibition, Los Angeles, CA, May 7-10, 2018.

Board Flex Testing  AEC-Q200-005 specifies conditions and the size of the test board. “A failure is when a part cracks or causes a change in the parametric being monitored.”  M32535 allows for multi-chip boards. Failure criteria: C >+/-10% at δ = 2 mm.  Factors affecting test results:  Orientation of the component;  Attachment with Ag-epoxy absorbs stress;  Solder fillet height, and thickness under the chip;  Solder type (less cracking for Pb-free alloys)  MLCC material (X7R weaker than COG)  Larger chips experience greater stress and have greater susceptibility to cracking.  This test is widely used to address cracking during de-panelization.  Results are affected by variety of factors.  Conditions for using multi-chip boards need additional analysis. Presented by Alexander Teverovsky at the 2018 CMSE Components for Military & Space Electronics Training & 9 Exhibition, Los Angeles, CA, May 7-10, 2018.