Article and Case Study Archive

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Foresite and BAE presentation from APEX 2007
An exploration of Cleanliness Assessment Correlation to Electronic Hardware Reliability. PowerPoint and PDF download available.

 

Articles

Download full-length articles discussing problem resolutions in which Foresite has participated. Many of these articles were written by Foresite President Terry Munson. For more recent articles, visit our blog.

 

Tin Whiskers on PCBA Capacitors in Storage
The tin whisker failures investigated in this paper occurred on functional RoHS-compliant hardware.

 

Fluoride Analysis by Ion Chromatography
Now You See It, Now You Don’t – This article discusses ion chromatography (IC) analysis and the importance of understanding the column’s capabilities and separation techniques to ensure accurate IC data.

 

Process Residues Cause Field Performance Problems
This is a look into how severe the consequences of ionic contamination can be to product performance. A study was done to show how ion chromatography results correlate to those of SIR, but that ROSE testing results show no correlation to either ion chromatography or SIR testing.

 

Residue Effects of Weak Organic Acid (WOA) Flux Activators
Flux chemistries that are not properly activated or cleaned are the most common sources of detrimental ionic contamination. This white paper compares and contrasts the various flux chemistry types available, and what their potential effects are on long term product reliability.

 

The Failure of a Circuit
This article discusses the various failure mechanisms that are regularly caused by harmful ionic contaminants reacting with moisture and an applied voltage.

 

Does Conformal Coating Stop Electrical Leakage Problems?
This analysis shows that conformal coating is only effective if there are no ionic residues entrapped underneath – though conformal coating may slow the absorption of moisture, it does not, over time, prevent moisture absorption and reaction with ionic contamination.

 

Power Module Failures: The Problem with Zinc Whiskers
An interesting study on how zinc (and tin) whisker growth directly correlates with concentrations of ionic contamination.

 

How Clean is Clean?
A study that examines how ion chromatography with C3 localized extraction correlates well with product performance while ROSE testing can overlook pockets of contamination.

 

Process Control and Qualification of Cleanliness Issues
A DOE study showing how C3 testing and extraction techniques can be incorporated into an effective process qualification protocol.

 

Terminal Block Manufacturing Residue Issues
Provides data and recommendations on manufacturing boards with terminal blocks.

 

PCB Contamination & Reliability DOE
This article was written by a client of ours, Phoenix International, and incorporates our data and findings to implement cleanliness parameters in electronics manufacturing.

 

Can You Clean a No-Clean?
This article looks at a specific case involving NTF returns with a client using a no-clean process, and looks at developing a successful cleaning protocol for assemblies constructed with a no-clean process.

 

Case Studies

Download case studies discussing problem resolutions in which Foresite has participated. Some case studies were published in Circuits Assemblies; others have been published in various locations.

 

White Residues – Are They or Aren’t They?
When it comes to white residues, a defect is not always a defect.

 

Know Your Sources
When it comes to contaminants, what you do not know can hurt you.

 

No Silver Lining
Sulfate contamination causes visible silver crystalline growth.

 

Stray Voltage on Low Standoff Components
The “Process Doctor” diagnoses an acute weak organic acid problem.

 

Not-So-Fine Debris
Left uncleaned, even staging racks can be a source of failures.

 

The Downside of Selective Soldering
If not cleaned, pallets can leave harmful residues.

 

What’s My Risk?
Determining the root cause of a field failure.

 

Do Electronics Really Have a Surface Contamination Problem?
As field returns mount, our answer is yes!

 

Environmental Chamber Cleanliness is Critical
Environmental screening can only be effective if equipment is clean and in control.

 

Localized Contamination, Big Problems
Localized ionic residues can be overlooked by bulk ionic testing methods.

 

Destructive Testing for Reconstructing Processes
Cross-sectional analysis is sometimes necessary in order to detect specific types of cracks and stresses.

 

Mean Green Corrosion
Selective soldering on ImAg boards built with a no-clean process can be a very touchy situation.

 

Keep It Clean!
Environmental chamber cleanliness has a direct impact on product performance.

 

On a Flat Note
Flat leadless PQFN package traps flux from no-clean solder paste leaving a gooey, conductive residue that caused product field failures due to electromigration.

 

Escape Artist
Design changes involving a standoff allow for flux trapped under a PQFN to volatilize and escape.

 

Clean It Up!
Incoming bare board and component cleanliness is crucial in building reliable product.

 

Let it Flow
A short reflow profile causes flux entrapment under low standoff components.

 

The Key to Success
Examine key parameters for a successful no-clean assembly.

 

Is White Residue a Reliability Risk?
This case examines a visible white residue and explains how to determine whether or not a white residue is detrimental.

 

Activate That Flux
The importance of full heat activation of fluxes to prevent detrimental weak organic acid (WOA) flux residues is emphasized in this case study.

 

Good Bonds Take Time
Inadequate reflow profiles cause weak joints and flux residues.

 

Understanding Specific Area Cleanliness
Ionic contamination can cause a wide array of failures. This article contains pictures of many such failures.

 

Can You Clean a No-Clean Assembly
Yes, you can clean a no-clean assembly!

 

Component Cleanliness in a No-Clean World
With a no-clean assembly process, the component, board and flux used in assembly are critical variables that must be understood and controlled.

 

Understanding Selective Pallet Soldering Residue
Proper heating can eliminate flux concerns.

 

Low Battery
Localized screening tests help pinpoint the cause of battery leakage failures.

 

Dark Conductive Residues
Examining the impact of sulfur contact on copper traces.

 

Finding Residue Sources
Finding residue sources in PCBs using Six Sigma techniques and using the Six Sigma inter-ocular test to find residue sources in PCB fabrication.

 

Other case studies we have written:

Solderability Problems: Both Residue & Thermal Conditions
Higher thermal mass boards require close examination of soldering profiles and solder deposition.

 

Ventilation Condensation
The cleanliness of environmental chambers has a direct impact on product performance.

 

Leakage, Leakage Everywhere
In this case study, we examine the effects of surface and absorbed fabrication residues on an assembler’s operation.

 

Garbage In = Garbage Out
In this case study, we examine the effects of elevated bromide from the fabrication process on an assembler’s qualification process.

 

The Crystalline Entity
In this case study, we examine detrimental residues present in a water soluble flux assembly process.

 

What, Me Worry About Fumes?
Low solids fluxes are finding increasing usage around the world. The cost savings afforded by the elimination of the cleaning operation is often attractive, but the world of no-clean fluxes poses many dangers for the uninformed.

 

The Mask from Hell
A manufacturer of a low-end commercial product was experiencing a wide-spread failure during burn-in testing. The failure mechanism was excessive leakage currents and an almost instantaneous metal migration situation.

 

Remedial Cleaning of the Mask from Hell
This is a follow-on to case study, The Mask from Hell.

 

When a Cool Flux Should Be a Hot Item
In this study, we worked with an assembler who was attempting to qualify a hand soldering process to J-STD-001 A, Appendix D and F guidelines.

 

Talk About Being Canned
In this study, we were attempting to help an assembler track down the cause of extensive corrosion on a printed wiring assembly.

 

But I’m Wearing Finger Cots!
Every once in a while it is good to examine assumptions you (or your management) have made in your manufacturing process. This case study involved handling residues.

 

I Could Solder to Concrete
In this study, we see what can happen when you use an active flux totally outside of the manufacturer’s recommendations.

 

Peelable Mask, Unpeelable Residues
In this study, we examine the effects of temporary processing materials, in this case a peel-able latex temporary solder mask.

 

That Darn Casting
In this study, we examined outside factors which were causing circuit failures during power temperature cycling (burn-in acceptance test).

 

Pop, Sizzle and Fry
In this study, we examined the cause of laminate blistering in aqueous cleaned assemblies.

 

Doing Everything Right and Still Failing Qualification Testing?
In this study, the assembler was examining different combinations of conformal coatings and OA fluxes, using qualification guidelines of MIL-STD-2000A, Appendix A.

 

Just Call Me Fireproof
In this study, we examine the effects of high levels of bromide residues on circuit boards, and how much bromide is a hazard.

 

I’m Surprised You Have Any Leads Left!
This is a case study involving component manufacturing and the residues involved.

 

Just Crank Up the Pressure
We look at a cleaning study that focuses on two misconceptions: (1) that you get better cleaning by increasing the spray pressures; and (2) that global board extractions will always tell you if you have a contamination problem.

 

Sure Hope We Don’t Get Caught
We love this line of work. We get to see all different kinds of manufacturing processes, some done exceptionally well, and some done exceptionally poorly.

 

What a Difference a Little Soap Makes
Anyone who has small children can tell you that if you want to get the kids clean after a day of playing, water alone will not do it.

 

On the Average, I’m OK
In this case study, we look at a problem concerning corrosion, metal migration, and electrical leakage, potentially affecting over 100,000 assemblies (field and inventory) with more being produced daily.

 

Bare Board Roulette
This is the second of a two-part study. In part 1 (March 1998), assemblies experienced high levels of corrosion, electrical leakage and metal migration.

 

We’re All Fed Up
Every once in a while, when doing failure analysis, it becomes necessary to try to recreate a failure mechanism in order to determine the basic problem.

 

No More Than I Have To
Anyone with a teenager is occasionally amazed at the effort put forth to avoid work.

 

It Always Works for the Repairman
One of Murphy’s Laws says that any broken appliance will always work when demonstrated for the repairman.

 

Parts Per Part
We love client facility visits. It gets us out of the everyday routine and exposes us to different cultures.

 

Microcanyons
Nearly all electronics assemblers make some sort of surface mount or mixed technology assembly.

 

A Problem with Teflon Insulation
Most of us consider polytetrafluoroethylene (PTFE or Teflon) to be a fairly inert or benign material.

 

Sulfate in Vias II
In a previous column, we examined the problem that an assembler was having with high levels of sulfate remaining in small diameter (less than 3 mils) vias. In this case study, we continue examining sulfates in vias.

 

Residues vs. SIR
In considering whether an assembly is considered as “acceptable”, there are two basic schools of thought.

 

White Residue – Good or Bad
This case looks at how different water qualities and cleaning chemistries affect the appearance of white residues and the cleaning effectiveness of BGAs. The second part of this case talks about how many white residues are conductive but not corrosive, and often come from un-cleaned flux reacting with water or from soldermask absorbing cleaning chemistry.