Application Notes Surface Mount Chip Capacitors TERMINATIONS

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Application Notes Surface Mount Chip Capacitors TERMINATIONS

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Application Notes Surface Mount Chip Capacitors
TERMINATIONS
Nickel barrier terminations (Termination Code "V") recommended solder attachment applications barrier's increased ability resist silver leaching which occur after prolonged exposure soldering temperatures. Palladium-Silver terminations (Termination Code "P") recommended conductive epoxy wire bond attachment methods.
GENERAL
Multi-layer ceramic capacitor chips (MLC's) will exhibit excellent reliability characteristics providing that controlled assembly process appropriate circuit design techniques utilized. MLC's crystalline micro- structure these components most susceptible over-rigorous control process conditions. primary concern reducing MLC's exposure excessive thermal mechanical shock during circuit manufacturing. should noted that micro-cracks ceramic very difficult detect with normal post assembly visual electrical testing pose significant threat reliable field operation. this reason recommended that assembly qualification process employ suitable testing expose presence micro-cracking conditions.
BOARD LAYOUT DESIGN
Appropriate design, solder application, component orientation ingredients quality, defect-free soldering process. design greatly influences size shape final solder fillet which also dependent soldering method, solder amount, placement technique. Nominal designs solder reflow solder wave processes shown following page. These dimensional guidelines follow Component Bulletin convention. Note that reflow widths closely approximate component width. larger area result component movement relief solder surface tension during reflow. Note that wave width approximately 2/3's component width. This reduces probability oversized solder fillet during immersion solder wave where abundance solder readily available. Excessive transfer thermal mechanical stresses result from oversized solder fillets. Note recommended chip orientation relative solder wave shown, which reduces likelihood defective solder fillets caused shadowing. solder design guidelines represent recommended starting point Printed Circuit Board (PCB) design. Other process considerations which affect design tolerances component placement, solder paste screening, artwork.
CHIP SELECTION
Component size dielectric material selection based several factors including board space electrical requirements capacitance, voltage temperature coefficient. Generally trend select smallest component which will meet required electrical performance. Additionally, consideration should given accuracy surface mount automatic placement equipment. Currently, 0805 1206 MLC's most popular sizes. Also, 0603 accelerating. MLC's 1812 size suitable vapor phase, reflow, wave soldering. chips larger size wave soldering recommended incompatibility chip's mass with steep temperature gradient typically present this process. Large chips experience excessive thermal mechanical stress during wave soldering resulting ceramic micro-cracking reliability risks.
Johanson Dielectrics, Inc. reserves right make design, specification, price changes without notice. Datasheet JDIAPPS
Solder Wave
REFLOW SOLDER PADS
SIZE 0603 0805 1206 1210 1808 1812 1825 2225
(mm)
WAVE SOLDER PADS
SIZE 0603 0805 1206 1210 1808 1812
(mm)
(mm)
(mm)
(mm)
(mm)
(mm)
(mm)
(mm)
A(nom) B(nom) C(nom) D(nom) E(min) 0.045 0.050 0.030 0.130 0.030 (1.14) (1.27) (0.76) (3.30) (0.76) 0.065 0.040 0.050 0.130 0.030 (1.27) (1.02) (1.02) (3.05) (0.76) 0.075 0.045 0.085 0.175 0.030 (1.65) (1.02) (2.03) (0.41) (0.76) 0.110 0.045 0.085 0.175 0.030 (2.54) (1.27) (2.03) (4.06) (0.76) 0.095 0.045 0.140 0.230 0.030 (2.03) (1.27) (3.30) (5.84) (0.76) 0.145 0.048 0.135 0.230 0.030 (3.05) (1.27) (3.30) (5.84) (0.76) 0.280 0.045 0.140 0.230 0.030 (6.35) (1.27) (3.30) (5.84) (0.76) 0.280 0.045 0.185 0.275 0.030 (6.35) (1.27) (4.32) (6.86) (0.76)
(mm)
(mm)
(mm)
(mm)
(mm)
A(nom) B(nom) C(nom) D(nom) E(min) 0.024 0.048 0.030 0.126 0.030 (0.61) (1.22) (0.76) (3.20) (0.76) 0.039 0.049 0.050 0.148 0.030 (0.99) (1.24) (1.27) (3.76) (0.76) 0.045 0.054 0.085 0.193 0.030 (1.15) (1.37) (2.16) (4.90) (0.76) 0.069 0.054 0.085 0.193 0.030 (1.76) (1.37) (2.16) (4.90) (0.76) 0.060 0.055 0.140 0.250 0.030 (1.53) (1.40) (3.56) (6.35) (0.76) 0.090 0.055 0.135 0.245 0.030 (2.30) (1.40) (3.43) (6.22) (0.76)
TOMB-STONING CHIP MOVEMENT
Tomb-stoning draw bridging illustrated figure below. Tomb-stoning other undesirable chip movements result unequal surface tension forces exist molten solder wets terminations mounting pads. This tendency minimized insuring that factors both solder joints equal, namely; size, solder mass, termination size, component position heating. Tomb-stoning easily avoided through proper design, material selection proofing process.
SOLDER FILLETS
avoid detrimental effects thermal mechanical stress essential that solder fillet limited 2/3's overall height termination illustrated figure below. solder fillet controlled solder paste deposition design reflow vapor phase processes design knives wave process.
Terminations Solder Fillet Ceramic Body Solder Fillet
Mounting Pads Printed Circuit Board (PCB)
15191 Bledsoe Street Sylmar, California 91342 (818) 9800 (818) 6100
JOHANSON
Application Notes Surface Mount Chip Capacitors
REFLOW
general term "reflow" refers several methods used heating circuit that solder paste reflows, "wetting" contacts occurs. These methods include infrared, convection radiant heating. size solder fillet controlled varying amount solder paste that screened onto circuit. Recommended temperature profile limits solder reflow shown figure (2).
PRE-HEAT CYCLE
Proper preheating essential prevent thermal shock cracking capacitor. circuit assembly should preheated shown recommended profiles rate second within 100°C maximum soldering temperature.
SOLDERING TEMPERATURES
Solders typically utilized have melting points between 179°C 188°C. Activation rosin fluxes occurs about 200°C. Based these facts minimum peak reflow temperature 205°C 210°C should established. maximum peak reflow temperature 225°C should adequate most circumstances. Many reflow process profiles have peaks ranging from 240°C 260°C while MLC's withstand soldering temperatures this range short durations they should minimized avoided whenever possible. mounted multiple thermocouple M.O.L.E. profiling advised accurate characterization circuit heat absorption maximum temperature conditions.
SOLDER WAVE
Wave soldering perhaps most rigorous surface mount soldering processes steep rise temperature seen circuit immersed molten solder wave, typically 240°C. Recommended temperature profile limits wave soldering shown figure (3).
SOLDERING IRON
attachment with soldering iron discouraged process control limitations. event that soldering iron must used following precautions should observed. Preheat circuit 150°C contact ceramic with iron watt iron output (max) temperature (max) diameter (max) Limit soldering time sec.
VAPOR PHASE
typical vapor phase soldering process consists several temperature zones created saturated vapor from boiling liquid. circuit passes through zone vapor condenses solder paste, termination resulting heat transfer reflow solder paste. Vapor phase reflow produces consistent circuit heating with reflow occurring relatively lower temperature that determined known boiling point liquid used, typically 215°C. Recommended temperature profile limits vapor phase reflow shown figure (1).
COOL DOWN CYCLE
After solder reflows properly assembly should allowed cool gradually room ambient conditions. Attempts speed this cooling process immediate exposure circuit cold cleaning solutions result thermal shock cracking MLC.
Johanson Dielectrics, Inc. reserves right make design, specification, price changes without notice. Datasheet JDIAPPS
Temperature (°C)
Soldering Time Sec. Max. 215°C
FIGURE
Pre-heating Zone: °C/sec.
Gradual Cooling Room Temperature
VAPOR PHASE
Time (sec.)
Temperature (°C)
Soldering Time Sec. Max. 250°C
FIGURE
Pre-heating Zone: °C/sec.
Gradual Cooling Room Temperature
SOLDER REFLOW
Time (sec.)
Soldering Time Sec. Max. @260°C
FIGURE
Temperature (°C)
Pre-heat °C/sec.
Gradual Cooling Room Temperature
SOLDER
Time (sec.)
15191 Bledsoe Street Sylmar, California 91342 (818) 9800 (818) 6100

Application Notes Surface Mount Chip Capacitors TERMINATIONS

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