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)

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

Cheaper Materials Result of Cost-saving

• Low-quality inputs

• Short-cutting production methods

Laminates (cont.)

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

Multilayer Pressing

Sample Press Cycle

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

ML Pressing (cont.)

Failure Mode Long / Short Term

Excess Smear / Interconnect Defects Short & Long Term

Delamination Short Term

Via Disruption / Excess CTE Short & Long Term

Under 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

Over Cure of Prepreg

Delamination

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?

Auditing for ML Press Control

Drill Bit quality is most important starting point

• In-house or outsourced repointing

• Automated or Manual repointing

• Quality of inspection tools

Drilling

Drilling - Repointing

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)

Drilling

Failure Mode Effect

Rough Hole Wall Rough Plating / Blown Vias

Nail Heading of inner layers Broken inner layer interconnects after thermal exposure

Impacted Drill Debris Hole Wall Pull-Away

Excess Smear across interconnects Long-Term reliability of via connections decreased

Pink-Ring / Delamination Interconnect separations

Failure Modes of Incorrect Parameters

Can cause open vias and hole wall pull-away

Rough Hole Wall

Can cause broken interconnects

Nail Heading

Can cause hole wall pull away

Impacted Drill Debris

Can cause hole wall pull away

Impacted Drill Debris (cont.)

Can cause long term via reliability issues

Cross Section of Excess Smear SEM of Excess Smear

Excess Smear

Can cause interconnect Issues

Pink Ring / Delamination

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)

Auditing for Proper Drilling

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

Copper Plating

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)

Tensile Strength & Elongation

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

Variation Control

In addition to chemistry, plating system set-up contributes greatly to product quality

Following is a table outlining key parameters

Plating System Parameters

Action Effect

Plate panels one-high in the plating rack Reduced variation via smaller anode area

24” Anode-to-anode distance Optimal distance insuring production panel area is adequately covered by anode area--without being so far as to reduce effectiveness of anodes.

Water-submerged cathodes Eliminates possibility of reduced contact due to oxidation of mating metal areas

Chemical-submerged anode bars Eliminates possibility of reduced contact due to oxidation of mating metal areas

Mechanical agitation Promotes chemistry flow through holes

Vibration Helps remove air from microvias and blind microvias

Dual-sided rectification Delivers optimal amperage to each side of production panel

Advanced rectification Newer DC and reverse pulse rectifiers have more consistent energy flow

Reduced Amps per Square Foot (11-15 for DC plating) Plating at reduced ASF for longer cycle time reduces plating variation

Plating – Key Parameters

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

Review Cross Sections

Statistical Analysis on Supplier’s plating thickness records

• Determine if within acceptable Standard Deviation Range

Auditing for Plating (cont.)

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

Bare Board Cleanliness

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

Ionic Contamination

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

OEM / CM – How do I combat?

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

PCB FAB – How can they control?

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

Conclusion

• ???

• ysutariya@saturnflex.com

Questions

Thanks!