Polymer Termination An alternative termination material specifically designed to absorb greater levels of mechanical stress thereby reducing capacitor failures associated with mechanical cracking Mechanical Cracking 2 The reason for polymer termination What is Polymer Termination? 3 Reducing capacitor susceptibility to Mechanical Cracking Validation Tests Performed 4 How Syfer has validated polymer termination Key Electrical Characteristics 8 Application Notes for Customers 9 Ordering Information 9 Syfer Product Code Construction Seite 1 von 10
Mechanical Cracking (The Reason for Polymer Termination) Due to its brittle nature, multilayer ceramic capacitors are more prone to excesses of mechanical stress than other components used in surface mounting. One of the most common causes of capacitor failures is directly attributable to bending of the printed circuit board (PCB) after solder attachment. Excessive bending will create mechanical crack(s) within the ceramic capacitor. Mechanical cracks, depending upon severity, may not cause capacitor failure during the final assembly test. Over time moisture penetration into the crack can cause a reduction in insulation resistance and eventual ielectric breakdown leading to capacitor failure in service. Fig 1. Mechanical Crack Example of capacitors issued by customers to Syfer for failure investigation: Capacitor Body and Electrodes T erm ination Force C rack Initiation Solder F illet Substrate Yellow potting compound Mechanical crack Electrical failure site Standard termination material (not polymer) Electrodes Seite 2 von 10
What is Polymer Termination? In order to reduce the possibility of mechanically cracking multilayer ceramic capacitors Syfer in conjunction with customers has been actively developing a new termination material. This termination is a silver loaded epoxy polymer that is flexible and absorbs some of the strain between the PCB and the ceramic capacitor. The termination is applied using conventional termination techniques, but instead of being sintered at approximately 800 C, the polymer is cured at 180 C. The polymer material has very good adhesive and conductive properties that are obtained after curing. After the polymer termination process stage the capacitors are plated with Nickel and Tin using the same methods as for the industry standard sintered Silver terminated capacitors. Fig 2. Capacitor Cross-Section Picture taken at 1000x magnification using a SEM showing a fracture section through a capacitor termination. The picture demonstrates the fibrous nature of the polymer termination that absorbs greater levels of mechanical stress when compared with standard sintered silver termination. Seite 3 von 10
Validation Tests Performed Before any new material is approved for use rigorous evaluation is conducted though Syfer s formal Design and Development process. The Design and Development process is used to ensure that new materials are evaluated, and where acceptable, introduced in a controlled and systematic manner. Validation of polymer termination has included:- Bend Test Trials. Samples of capacitors are mounted onto FR4 Test PCBs using 62/36/2 Sn/Pb/Ag solder and subjected to bend testing in accordance with IEC 384-1 Fixed Capacitors for use in Electronic Equipment section Bond strength of the face plating. Example of FR4 Test PCB Used Material: Board Thickness: Copper Coating Thickness: FR4 (Glass Fiber Epoxy) 1.6mm 0.035mm Capacitor Placement Method Seite 4 von 10
Hand pick and place used to mount capacitors for bend tests. To enable polymer termination performance to be compared with standard sintered silver termination, samples of capacitors were taken from capacitor batches for evaluation. The first sample was terminated with polymer termination and the second sample terminated with standard silver termination. The same capacitor batches were used for both the polymer termination and standard termination bend tests. Syfer s Bend Test Facility PCB Position Seite 5 von 10
Press Head 20mm Depth: 50mm Radius: 340mm Capacitor 90mm A total of 16 Test PCBs are used for each bend test. Each PCB is mounted with either 2, 3 or 5 capacitors depending upon capacitor size and 4 Test PCBs are used for each deflection depth. After the PCBs have been deflected, capacitors are carefully removed using a hot air pencil and microsectioned to determine the presence of mechanical cracks. For example, bend tests results from samples taken from Syfer batch number X09514 (2220 50 volt 1uF X7R): BEND mm STANDARD % CRACK POLYMER % CRACK 2.5 0 Not tested 3 50 0 4 100 0 5 100 0 6 Not tested 50 MEAN BEND mm 2.75 5.75 Seite 6 von 10
Multiple samples have been evaluated across Syfer s X7R 0805, 1206, 1812 and 2220 ranges with the following results: capacitor PRODUCT MEAN BEND (mm) STANDARD TERM. MEAN BEND (mm) POLYMER TERM. 0805 X7R 3.6 6.3 1206 X7R 3.4 6.4 1812 X7R 3.2 6.0 2220 X7R 3.2 6.1 The bend tests conducted have proved that the polymer termination withstands a greater level of mechanical stress before mechanical cracking is created. Load Test Trials As part of the development process fifty capacitors from over 10 lots of polymer terminated X7R product were subjected to 1.5x Rated Voltage @125 C for 1000 hours. No capacitors failed as a result of polymer termination failure. As of March 2001 a total of 1277600 components test hours have accumulated. During this period only 1 capacitor failed and this failure was not attributed to the polymer termination. Seite 7 von 10
X7R Polymer Termination FIT Rates Calculated at 60% Confidence Level 100000 1000 10 FIT's 0.1 0.001 0.00001 Temperature 10% of RV 25% of RV 50% of RV RV 25 C 50 C 75 C 100 C 125 C 0.000 0.001 0.016 0.148 1.045 0.001 0.014 0.188 1.757 12.406 0.005 0.092 1.222 11.420 80.613 0.029 0.601 7.939 74.207 523.828 Data derived from 1277600 component test hours from which there were 1 failures. FIT = Failures in 10 9 Hours Reliability Unit Conversion Factors: Failures in 10 6 Hours: Divide FITs by 10 3 % failures in 10 3 Hours: Divide FITs by 10 4 By using the FIT rate data customers can evaluate the expected failure rate of capacitors (calculated at 60% confidence level) by comparing the % of RV (Rated Volts) being applied with the operating temperature. For example, if a 100V rated capacitor is being used by a customer at 10V (10% of RV) @ 75 C then by using the table the FIT rate is 0.016. Note: The table has been calculated using a variety of product codes terminated with polymer termination. Humidity Test Trials Humidity tests consist of subjecting sample size of fifty capacitors to 85 C @ 85RH for 168 hours. Over 30 samples of polymer terminated capacitors have been tested with 0 failures. Seite 8 von 10
Customer Trials. Samples of polymer terminated capacitors have been supplied to customers for assembly trials. The trials conducted by customers have been successful and customer reaction to the introduction of polymer termination has been extremely favorable. Over the last 12 months the demand for polymer terminated capacitors has been rapidly increasing as customers realize the advantages provided. Customers supplied to include Ericsson, Siemens, Power One, Tyco, Convergie and component distributors. In addition to the validation tests performed, tests now conducted at Syfer include:- Bend test trials on each new lot of polymer termination submitted to Syfer. There have been 0 polymer termination lots rejected. Routine load testing, humidity testing and bend testing on samples of production capacitor batches manufactured. Polymer termination has not caused any capacitor failures. Key Electrical Characteristics Polymer terminated capacitors have slightly improved Dissipation Factor (DF), Equivalent Series Resistance (E.S.R.) and Inductance measurements. For example: Capacitance @ 1kHz DF @ 1kHz E.S.R. @ 1MHz Inductance @ 1MHz Standard 2.5414nF 0.000205 0.0419Ω -9.9722uH Termination Polymer Termination 2.5418nF 0.000182 0.0350Ω -9.9691uH Seite 9 von 10
Application Notes Polymer terminated capacitors should be handled, stored and transported in the same manner as standard terminated capacitors. The requirements for mounting and soldering polymer terminated capacitors are the same as for standard terminated capacitors. For customers currently using standard terminated capacitors there should be no requirement to change the assembly process when converting to polymer termination. Based upon board bend tests in accordance with IEC 384-1 the level of stress required to mechanically crack a polymer terminated capacitor is effectively double when compared with a standard terminated capacitor. It must be stressed however, that capacitor users must not assume that the use of polymer terminated capacitors will totally eliminate mechanical cracking. Process controls are still required for this objective to be achieved. Ordering Requirements Syfer product code construction:- Example:.. 1210 Y 100 0103 J X T _ Type No/Size ref Suffix code. Used for specific customer requirements. Termination F = Silver Palladium Packaging. J = Nickel Barrier (standard) T = 178mm (7 ) reel Y= Polymer R = 330mm (13 ) reel Special terminations B = Bulk pack - tubs A= High Leach Resistant Silver Palladium Dielectric code Voltage Rating d.c. Capacitance Value (pf) Capacitance tolerance code Seite 10 von 10