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Arc Season & Board Design Observations
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- Causes of Arc Failures – Seasonal arcing in high-voltage assemblies is often tied to board layout, flux residues, humidity absorption, and solder paste choice. Water-soluble flux, if not fully cleaned, leaves residues that lower arc voltage and increase leakage, leading to field failures.
- Design & Process Recommendations – Improve AC breakdown performance by eliminating solder mask between pads, avoiding slots where possible, adding pad corner radiuses, and ensuring thorough cleaning. Careful PWB design and flux management help minimize arcing risks in HV capacitor applications.
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Basics of Ceramic Chip Capacitors
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- How MLCCs Are Made & Specified – Covers the manufacturing process (slurry prep, tape casting, stacking, firing, plating, testing), the difference between precious metal vs. base metal systems, and critical specs like dielectric constant, dissipation factor, insulation resistance, and withstanding voltage.
- Key Characteristics – Explains the advantages of MLCCs (low ESR/ESL, low impedance at high frequencies) along with performance factors such as temperature coefficient, voltage coefficient, and aging effects, giving engineers a clear understanding of trade-offs between NP0, X7R, and Y5V materials.
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Capacitor Cracks: Still with Us After All These Years
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- Persistent Issue – While improved pick-and-place and soldering processes have reduced cracking risks, board flexure during handling, testing, and assembly remains the leading cause of MLCC cracks, which can create latent defects or catastrophic failures.
- Design & Handling Solutions – Following PWB layout best practices (keeping capacitors away from stress zones, edges, connectors, and mounting holes), avoiding wave/hand soldering on large parts, controlling solder mask use, and careful handling all significantly reduce cracking risks.
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Capacitor Packaging
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- Standard Packaging – Johanson capacitors are supplied taped per EIA-481, with options for 7” and 13” reels, using dust-free punched 8 mm paper tape or embossed plastic tape for thicker MLCCs.
- Reel Quantities – The number of parts per reel depends on chip thickness and tape type; reference tables provide typical ranges, and sales can confirm exact quantities for specific part numbers.
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Ceramic Capacitor Aging Made Simple
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- Class II Aging Phenomenon – Dielectrics like X7R, X5R, and Y5V lose capacitance over time due to crystalline realignment, with predictable rates (≈ -2.5% per decade hour for X7R/X5R, -7% for Y5V). In contrast, Class I dielectrics (NP0/COG) remain stable but offer lower capacitance values.
- De-Aging & Testing Considerations – Aging is reversible by heating above the Curie Point (~125 °C), restoring capacitance to its initial value. Manufacturers test capacitors with adjusted limits at 1000 hours, and engineers should account for post-soldering “de-aging” effects and stabilization time when measuring capacitance.
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Corona Effects & PWB Layout Impact on HiPot Failures
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- Root Cause of Failures – Corona discharge during HiPot testing often results from solder mask limitations, flux residues, and capacitor body acting as a pseudo electrode, which reduces isolation distance and can trigger partial discharges, arcing, or dielectric breakdown.
- Design Guidance – Avoid traces, vias, or pads under isolation capacitors; do not rely on solder mask for insulation; and carefully evaluate creepage, spacing, and capacitor placement to ensure reliable high-voltage performance in assemblies.
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DC-DC Converter Trends & Output Filter Capacitors
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- Reviews evolving DC-DC converter designs that demand capacitors with low ESR/ESL and high ripple current handling.
- Highlights how Johanson MLCCs provide efficient output filtering compared to traditional electrolytic solutions.
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Forward/Backward Process Compatibility
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- Explains differences between base-metal vs. precious-metal electrode MLCCs and their firing atmospheres.
- Details compatibility considerations for designers mixing capacitor types in the same assembly.
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Peak Reflow Times, Temperatures, & Impact of MSL
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- Summarizes industry guidelines for reflow soldering profiles and the effect on moisture sensitivity levels (MSL).
- Advises on safe processing windows to avoid cracking, delamination, or reliability issues.
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Sn/Pb SMT Application Notes
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- Provides guidelines for soldering MLCCs with Sn/Pb solder alloys.
- Covers temperature profiles, solder joint reliability, and handling precautions for mixed-technology assemblies.
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Solder Reflow Recommendation for Lead-Free Assembly
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- Outlines best practices for RoHS-compliant lead-free reflow soldering.
- Addresses higher melting temperatures, controlled heating/cooling rates, and minimizing thermal shock to capacitors.
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Pad Design & Spacing Impact on AC Breakdown
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- Demonstrates how pad geometry, solder mask use, and spacing affect high-voltage breakdown performance.
- Recommends optimized pad layouts to minimize corona effects, arcing, and HiPot failures.
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Tin Whisker Testing
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- Reviews Johanson’s testing of tin whisker growth on terminations.
- Confirms reliability of plating finishes and provides guidance for long-term risk mitigation in high-reliability applications.
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Amplifier Decoupling: EMI vs MLCC
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- Compares Johanson’s EMI filter capacitors to standard MLCCs in amplifier decoupling.
- Shows EMI capacitors achieve up to 280–350% lower noise voltage with fewer parts and reduced cost.
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PCB Pad Layout Recommendations
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- Covers pad sizes, spacing, and solder fillet control to ensure reliable solder joints.
- Includes guidance on minimizing mechanical stress that can cause capacitor cracking during reflow or handling.
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Recommended Storage Conditions
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- Lists environmental requirements for long-term capacitor storage before assembly.
- Emphasizes humidity and temperature control to prevent oxidation or degradation.
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Part Number Explanation
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- Breaks down Johanson’s capacitor part numbering system into clear segments.
- Each section of the code represents attributes such as dielectric, capacitance value, tolerance, case size, termination, and voltage rating.
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