To Kill A Circuit Board: Perils

in Manual Soldering &

Cleaning Processes

Cheryl Tulkoff, ASQ CRE

Senior Member of the Technical Staff

DfR Solutions

ctulkoff@dfrsolutions.com

SMTAI 2014

Rosemont, Il

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Manual soldering and cleaning processes are among the least controlled

processes in printed circuit board assembly

As a result, they create special challenges to both quality and long term

reliability

This presentation describes some of those key challenges and provides ways to

address them in assembly to minimize problems. Topics to be covered include:

Design Considerations

General Manual Soldering Recommendations

Material Selection and Qualification Criteria

Cleaning Recommendations

Process Monitoring and Control

Relevant Industry Standards

Case Study

Through awareness of the issues, proper design and appropriate material

selection and process control, companies can successfully use manual

soldering and cleaning processes in high reliability products.

Without proper planning, however, these processes can lead to a path of ruin.

Abstract

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Surface finish & type

Pin Through Hole (PTH) Fill

Copper Dissolution

Component Selection &

Placement

Key Design Considerations

3

Surface Finish Challenges

Surface Finish Manual Soldering Challenges

ENIG (Electroless nickel ,

immersion gold) and

ENEPIG (electroless Pd added)

Slightly less solder spread,

incomplete pad coverage

Immersion silver (ImAg) None

Immersion tin (ImSn) None

Organic solderability preservative

(OSP)

Incomplete pad coverage, PTH hole

fill, copper dissolution

Pb-free HASL (SAC) Copper dissolution

Pb-free HASL (Silver-free) None

4

OSP Issues: Hole Fill

OSP has lower wetting force

Risk of insufficient hole fill

Solutions:

Changing board finish

Increasing top-side preheat

Increasing solder pot

temperature

Changing wave solder alloy

P. Biocca, Kester

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PTH Soldering: Incomplete Hole Fill o Poor solder hole fill can lead to solder joint cracks/failures

o Can be caused by: o Insufficient top side heating prevented solder from wicking up into PTH Barrel

o Insufficient flux or flux activity for the surface finish in use

o Lack of thermal relief for large copper planes

o PCB hole wall integrity issues – voids, plating, contamination

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PTH Hole Fill & Thermal Relief Utilize thermal reliefs on all copper planes when practical

Reduces thermal transfer rate between PTH and copper plane

Allows for easier solder joint formation during solder (especially for Pb-free)

Allows for better hole fill

Copper

Plane

PTH

Laminate

Copper

Spoke

Courtesy of D. Canfield (Excalibur Manufacturing) 7

Solders: Copper Dissolution

Reduction or elimination of

surface copper conductors

due to repeated exposure to

Sn-based solders

Significant concern for

industries that perform

extensive manual soldering

or rework

Bath, iNEMI

ENIG Plating

60 sec. exposure

274ºC solder fountain

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Solders: Copper Dissolution (cont.)

PTH knee is the point of

greatest plating reduction

Primarily a rework & repair

issue

Already having a

detrimental effect

S. Zweigart, Solectron

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Copper Dissolution & Contact Time

Contact time is the major driver

Some indications of a 25-30 second limit

A Study of Copper Dissolution During Pb-Free PTH Rework Using a

Thermally Massive Test Vehicle , C. Hamilton (May 2007)

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Component Selection Considerations

Lead Size

Lead Plating

Lead Type PTH

Blunt or blade

Tapered

Lead must protrude

Lead to hole ratio Rule of thumb for PTH fill

Hole needs to be .008” to .020” larger than the lead

Refer to IPC-2221 Industry Standard for Printed Board Design

http://www.ipcoutlook.org/mart/50190F.shtml 11

Impact of Component Plating on

Solderability Metal

Surfaces

Solderability

Platinum

Gold

Copper

Tin

Solder

Palladium

Silver

Easy to Solder

Nickel

Brass

Cadmium

Lead

Bronze

Rhodium

Beryllium

Copper

Less Easy to Solder

Nickel-Iron

Kovar

Difficult to Solder

Difficult to solder

platings drive use of

more aggressive

process chemistries

Increases risk of

residue issues

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Component Spacing

Allow for adequate

spacing for manual

attach and repair

Avoid thermal damage

& thermal shock

Ceramic Cracks

Electrolytic caps

Solder mask & circuitry

Finetech BGA Attach

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Ceramic Caps: Thermal Shock Cracks

o Due to excessive

change in temperature

o Maximum tensile stress

occurs near end of

termination

o Three manifestations

o Visually detectable

(rare)

o Electrically detectable

o Microcrack (worst-case)

NAMICS

AVX

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Thermal Shock Crack: Micro Crack

o Variations in voltage or

temperature drive crack

propagation

o Failures identified as o Increase in electrical resistance

o Decrease in capacitance

DfR

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Operator variation is the norm

Training is critical!

General manual soldering tips:

Use soldering irons with the greatest thermal

recovery

Use the largest tip for the size of the joint being

soldered and with the available working space

Use custom tips as needed

Use the largest cored solder wire diameter for the

size of the joint and available working space

Manual Soldering Recommendations

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Solder Tip Size & Cored Wire Size

Recommendations

Images courtesy of OK International

The diagram below shows why No-Clean Flux-cored solder seldom works as well

as RMA-cored solder:

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Manual Soldering Accessories

Images show tools

which must be routinely

replaced or cleaned to

prevent cross-

contamination

Needle tip flux dispense

not recommended

Poor control over volume

& flow

Different solder alloys

should not use the same

materials

Needle tip flux dispenser

Solvent dispense bottle

Sponge

Tip Cleaner

Cleaning Brush

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Use a portable preheater to shorten contact time and fully activate fluxes http://www.zeph.com/airbathseri

es.htm

Verify actual PCB and lead temperatures with small temp labels http://www.omega.com/toc_asp/

sectionSC.asp?section=F&book=temperature

Manual Soldering Accessories

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Solder preforms can be placed on a pad or on a PTH lead on the topside of the PCB

Repeatable joints on both PTH and SMT joints

Assist in getting complete PTH fill

Controls both volume of solder & volume of flux applied

Can be made in size, alloy, and flux of choice

Preforms for Soldering Uniformity

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Designed for manual soldering processes

SIR data available

Halogen / halide free

Supplier: relationships, proximity

Lead finish

Substrate finish

Lead free or SnPb soldering

Compatibility with adjacent materials Adhesives, conformal coatings, etc.

Manual Soldering Materials

Selection Criteria

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Avoid liquid flux in manual soldering if

possible but if it’s truly needed:

Look for methods to ensure precise delivery

Flux pens

Needle tip dispense bottles are not recommended

Avoid letting flux run under and around adjacent

components

Provide some form of uniform heating to volatalize

as much of the liquid as possible

Avoid Using Liquid Flux

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Process Material Qualification

Recommendations Validate compatibility and performance of all new

process materials using SIR testing

IPC-B-52 SIR TEST VEHICLE

IPC-A-52:Cleanliness and Residue Evaluation Test

Board – Single User CD-ROM

The IPC-B-52 test board is intended to be a

process qualification vehicle

Materials of construction and source of test boards

to be representative

https://portal.ipc.org/Purchase/ProductDetail.aspx?

Product_code=5e7a8626-b486-db11-a4eb-

005056875b22

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IPC-B-52 (IEC TB-57) The latest generation of test coupons

Main SIR Test Board

IC Test Coupon

Solder Mask Adhesion

SIR mini-coupons

Packages 0402 – 1206

QFP (no 0.4mm pitch)

SOICs and BGAs

Through-Hole Header

Comb patterns (5 mil)

Not specifically called out in any TM-650 test method 24

Typical manual cleaning process:

Solder fillets are cleaned following the solder operation

Some type of solvent spray is used to loosen flux residues

Followed by manual cleaning using IPA and a soft bristle

brush

This type of manual cleaning process represents a

reliability risk

Brushes are not routinely cleaned or maintained

Become contamination transfer mechanisms

Poorly removed residues are more likely to experience

corrosion failures than no clean flux residues left intact

In rework and repair, if you can’t rinse, you can’t clean!

Manual Removal of Flux Residues:

Not Recommended!

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When to Clean? Very high reliability applications

Medical, Military, Avionics, Industrial, Telecom

Sensitive circuitry High-impedance circuits

High-frequency circuits

Operation in uncontrolled environments

Use of conformal coating Concerns over compatibility

Cleaning improves adhesion

Note: Some high-reliability markets have moved away from cleaning Automotive, Enterprise, etc.

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Industry Standards on PCBA

Cleaning Requirements driven by J-STD-001

Mandates 10ug/in2 (1.56 ug/cm2) NaCl equivalent conductivity for ROL0 or ROL1

Others based on limit established by user

Section 6.1

Assemblies should be cleaned after each soldering operation so that subsequent placement and soldering operations are not impaired by contamination

Section 8.2.2

Cleanliness testing is not required (unless specified by the customer)

SPC not required (testing should be random, but sample plan not provided)

If any assembly fails, the entire lot shall be evaluated and re-cleaned and a random sample of this lot and each lot cleaned since performing the last acceptable cleanliness test shall be tested

Some guidance provided by two handbooks

Guidelines for Cleaning of Printed Boards and Assemblies, IPC-CH-65B (2011)

Aqueous Post Solder Cleaning Handbook, IPC-AC-62A (1996) 27

If flux residues must be removed

manually, a 4 step process is

recommended:

Wet, scrub, rinse, dry

Use some form of dispensing system

to control the flow of the cleaning fluid

Material is fresh and pure each time.

Replace brushes routinely

Clean better, more consistently and with

less solvent

Manual Removal of Flux Residues

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Critical Aspects of PCBA

Cleaning Solder Paste / Flux Chemistry

Component Selection and Board Design

Equipment Batch vs. Inline

Critical equipment parameters

Cleaning Solution Includes solvent, chemistry, and temperature

Process Location When to clean?

Cleanliness Requirements and Assessment 29

Cleaning Equipment

Two options In-line

Batch (dishwasher)

Batch cleaning tends to dominate In-line primarily justified based on volumes

High-volume manufacturing tends to not clean

Ultrasonic Cleaning Rarely used on PCBAs

Restrictions in J-STD-001

Outdated knowledge from early process failures

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Cleaning Process and Solution

Variables

Pure DI or Saponifier (type and concentration)

Temperature (120F to >175F)

Nozzle pressure and direction

Agitation (spray in air)

Time

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Test Procedures: Best Practice

Ion Chromatography (IC) is the ‘gold standard’

Some, but very few, PCB manufacturers qualify lots

based on IC results

Larger group uses IC to baseline ROSE /

Omegameter / Ionograph (R/O/I) results

Perform lot qualification with R/O/I

Periodically recalibrate with IC (every week, month, or

quarter)

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ROSE and Omega-Meter tests DO NOT detect

WOAs (weak organic acids)

Successfully passing these “cleanliness” tests

does not ensure cleanliness

ROSE and Omega-Meter are suitable for bare PCB

cleanliness testing and for finding halide residues

Ion Chromatography (IC) is only test that finds and

quantifies WOAs

No uniform/standard accept/reject limits

1/ Solvent Extraction Matrix Selection and its Potential Affects on Cleanliness Test Results, K. Sellers, J. Radman, Trace

Laboratories

Weak Organic Acid Detection

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Case Study

PTH Ecaps Close to Processor

Insufficient PTH Hole Fill on Cu OSP

Excess Flux from Manual Soldering

34

EC RAT – Anyone tried this?

http://www.ec-rat.com/

Residues Rat for detection of unreacted

flux residues from the soldering process

of electronics production

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Summary

Risks associated with manual soldering

can be reduced

Preparing for them early in the design phase

Optimize design practices

Select appropriate materials

Characterize materials, and

Monitor the process

These practices ensure robust results!

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Presenter Biography

Cheryl has over 22 years of experience in electronics manufacturing focusing on failure analysis and reliability. She is passionate about applying her unique background to enable her clients to maximize and accelerate product design and development while saving time, managing resources, and improving customer satisfaction.

Throughout her career, Cheryl has had extensive training experience and is a published author and a senior member of both ASQ and IEEE. She views teaching as a two-way process that enables her to impart her knowledge on to others as well as reinforce her own understanding and ability to explain complex concepts through student interaction. A passionate advocate of continued learning, Cheryl has taught electronics workshops that introduced her to numerous fascinating companies, people, and cultures.

Cheryl has served as chairman of the IEEE Central Texas Women in Engineering and IEEE Accelerated Stress Testing and Reliability sections and is an ASQ Certified Reliability Engineer, an SMTA Speaker of Distinction and serves on ASQ, IPC and iNEMI committees.

Cheryl earned her Bachelor of Mechanical Engineering degree from Georgia Tech and is currently a student in the UT Austin Masters of Science in Technology Commercialization (MSTC) program. She was drawn to the MSTC program as an avenue that will allow her to acquire relevant and current business skills which, combined with her technical background, will serve as a springboard enabling her clients to succeed in introducing reliable, blockbuster products tailored to the best market segment.

In her free time, Cheryl loves to run! She’s had the good fortune to run everything from 5k’s to 100 milers including the Boston Marathon, the Tahoe Triple (three marathons in 3 days) and the nonstop Rocky Raccoon 100 miler. She also enjoys travel and has visited 46 US states and over 20 countries around the world. Cheryl combines these two passions in what she calls “running tourism” which lets her quickly get her bearings and see the sights in new places.

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