Yash Sutariya President Saturn Electronics Corporation Glory Faith North America Saturn Flex Systems
Key Inputs to PCB Reliability Backbone Fabrication Processes Multilayer Press Via Drilling Copper Through Hole Plating PCB Cleanliness Original Articles: Built Board Tough - the pcb magazine (July 2012) DC Plating for High Reliability Applications the pcb magazine (January 2013) Cleaning Up Your Act SMT Magazine (September 2012)
Laminates Qualified through IPC 4101, Laminates meet a particular spec by testing characteristics Tg Td CTEs And now, the rest of the story Only 4-5 North American production laminate suppliers In China, there are in excess of 30 suppliers ranging the entire span of revenue levels
Laminates (cont.) Cheaper Materials Result of Cost-saving Low-quality inputs Short-cutting production methods
Multilayer Pressing Bonds individual layer cores (C-Stage) together using prepreg (B-Stage) Critical Parameters vary by material, but typically include: Rate of Rise through critical range Achieving Cure Temp Time at Cure Temp
Sample Press Cycle
ML Pressing (cont.) Failure modes: Under-Cure and Over-Cure Each has different impact on short and long term reliability Recipes need to be verified periodically as press components may cause variations over time
Under Cure of Prepreg Failure Mode Long / Short Term Excess Smear / Interconnect Defects Short & Long Term Delamination Short Term Via Disruption / Excess CTE Short & Long Term
Over Cure of Prepreg Failure Mode Long/Short Term Rough Hole Wall Short & Long Term Surface Embrittlement Short Term Via Disruption / Excess CTE Short & Long Term
Delamination
Auditing for ML Press Control Press Control Checklist Does the press have product thermocouple capability? Does it have a vacuum chamber? Does the PLC have capability to store product / build specific recipes? Does the QC Engineer maintain periodic test results showing that the actual temperatures match desired in both PLC and Product Process Guidelines?
Drilling Drill Bit quality is most important starting point In-house or outsourced repointing Automated or Manual repointing Quality of inspection tools
Drilling - Repointing
Drilling Key Factors vary by Material and Drill Bit Type Feed (Rate of Entry into Material) Speed (RPM of Drill Spindle) Retract (Rate of Exit out of Material)
Failure Modes of Incorrect Parameters Failure Mode Rough Hole Wall Nail Heading of inner layers Impacted Drill Debris Excess Smear across interconnects Pink-Ring / Delamination Effect Rough Plating / Blown Vias Broken inner layer interconnects after thermal exposure Hole Wall Pull-Away Long-Term reliability of via connections decreased Interconnect separations
Rough Hole Wall Can cause open vias and hole wall pull-away
Nail Heading Can cause broken interconnects
Impacted Drill Debris Can cause hole wall pull away
Impacted Drill Debris (cont.) Can cause hole wall pull away
Excess Smear Cross Section of Excess Smear SEM of Excess Smear Can cause long term via reliability issues
Pink Ring / Delamination Can cause interconnect Issues
Auditing for Proper Drilling How have feeds and speeds been determined? How many drill bit vendors are used? How many different types of materials are used? How are drilling parameters entered into the machine? Operator (High Risk) Drill Table in PLC (Medium Risk) Drill Room Management Software (Low Risk)
Copper Plating Primary Desired Outcomes High Tensile Strength and Elongation Properties Allow increased expansion and contraction of plating in hole wall under thermal conditioning Reduced Copper Plating Thickness Variation Allows thickness readings from samplings to be trusted for entire production lot Reduces the target set thickness to insure meeting minimum plating requirements
Tensile Strength & Elongation Easier-to-use chemistry often results in lower T&E s Chemistry component control is critical to optimizing plating performance Control Requires the following: Proper Test Equipment Frequent Testing Control and Monitoring of Inorganic Contaminants (Carbon Treating Schedule)
Variation Control Copper plating systems can be optimized to achieve either: Higher Throughput Higher Quality Key is to balance the two to achieve High Reliability at a Competitive Cost
Plating System Parameters In addition to chemistry, plating system set-up contributes greatly to product quality Following is a table outlining key parameters
Plating Key Parameters Action Plate panels one-high in the plating rack Effect Reduced variation via smaller anode area 24 Anode-to-anode distance Water-submerged cathodes Chemical-submerged anode bars Mechanical agitation Optimal distance insuring production panel area is adequately covered by anode area--without being so far as to reduce effectiveness of anodes. Eliminates possibility of reduced contact due to oxidation of mating metal areas Eliminates possibility of reduced contact due to oxidation of mating metal areas Promotes chemistry flow through holes Vibration Helps remove air from microvias and blind microvias Dual-sided rectification Advanced rectification Reduced Amps per Square Foot (11-15 for DC plating) Delivers optimal amperage to each side of production panel Newer DC and reverse pulse rectifiers have more consistent energy flow Plating at reduced ASF for longer cycle time reduces plating variation
Auditing for Plating Contact Suppliers of Plating Chemistry that your suppliers use for their opinion Audit Lab Records to confirm frequency of testing Submit Test Vehicles for Reliability Testing IST HATS Thermal Cycling Audit Setup against Ideal Setup Checklist
Auditing for Plating (cont.) Review Cross Sections Statistical Analysis on Supplier s plating thickness records Determine if within acceptable Standard Deviation Range
Bare Board Cleanliness Ionic Contamination can lead to dendrite growth Dendrites can cause massive shorting across PCB surface after time in the field Ionic Contamination is covered under IPC-5704 However, not often called out in PCB FAB Notes or OEM / CM PCB Specifications
Ionic Contamination Primarily a considerable factor in PCBs with HASL or Pb-Free HASL Final Finish Fluxes introduce most contaminants to the PCB surface Not detectable without Ionograph or Ion Chromatograph Will not result in immediate PCB failure Typically results in field failures in right conditions
OEM / CM How do I combat? Easiest method is to use conformal coating If conformal coating not being used: Pre-Clean PCBs Prior to Assembly Not typically feasible due to equipment and timing needs Introduces moisture to the boards Rely on my PCB Vendor to control the process
PCB FAB How can they control? Simple: Clean the Board! Easier to Clean when board is less dirty to start with UV Bumping after soldermask application closes pores that can entrap fluxes Use a saponifier or solvent-based mixture during post-hasl PCB cleaning This is a cleaning agent that breaks up and disperses flux residue from the PCB surface
PCB FAB How can they control? Mechanically Clean the Board Design or Purchase a lateral scrubbing mechanism for use during HASL post-cleaning Not an industry standard Use increased temperatures during scrubbing and rinsing Measure ionic contamination on a frequent basis This insures mechanisms and chemistries operating at effective levels
Conclusion Insuring PCB reliability is not an easy task Basic knowledge of key contributing processes makes PCB users dangerous auditors Characterizing PCB Suppliers Key Processes critical tool for managing Supply Chain
Questions??? ysutariya@saturnflex.com
Thanks!