Research
Innovative Panel Plating for Heterogeneous Integration
A Method to Investigate PCB Supplier Rework Processes and Best Practices
The Effects of PCB Fabrication on High-Frequency Electrical Performance
Aerosol Jet Printing of Conductive Epoxy for 3D
EOS Exposure of Components in the Soldering Process
High Thermo-Mechanical Fatigue and Drop Shock Resistant Alloys
Filling of Microvias and Through Holes by Electrolytic Copper Plating
NASA DOD Phase 2: Copper Dissolution Testing
MORE RESEARCH
Latest Industry News
How Telecom is Rolling Out 5G During a Pandemic
Can Software Performance Engineering Save Us From the End of Moore's Law?
Tech stocks have been a winning bet, but investors worry it will fade
All This Chaos Might Be Giving You 'Crisis Fatigue'
Notebook PCB makers to see tight capacity through 3Q20
How Effective Is Nano Coating On Stencils?
U.S. Critical Infrastructure Full of Security Holes
Auto Interior Is the New Exterior
MORE INDUSTRY NEWS

Role of Carbon Ink in Calculators



Role of Carbon Ink in Calculators
Texas Instrument's calculators made in the 80's used a flexible circuit made with carbon ink. What vital part did the carbon ink serve?
Mysteries of Science

Transcript


The printed circuit used in Texas Instruments' calculators built in the 1980's, was a flexible circuit made with copper conductors and Mylar plastic. The company was scrutinizing every aspect of manufacturing in an effort to cut costs as Japanese competition was becoming more intense. 

After much scrutiny a purchasing agent began to question a black ink used in the manufacturing process. No one could quite explain what the carbon ink did, but it had always been there.

One hundred circuits were made with no black ink for testing. The calculators manufactured using this carbon inkless circuit worked, but turning them on was no small chore.

QA claimed that certification for the change would take months and be quite costly. To bypass this, the purchasing agent stated that it was a graphics change. QA allowed this to proceed without any further testing, but three months later the purpose of the black ink was clear.

What was the vital part of the manufacturing process that the carbon ink served?

Here's the rest of the story.

The carbon ink that was deleted had been put there to perform specific functions and should have never been eliminated. It created a smooth, compliant, and compatible contact to the glass LCD panel, but it also prevented the solder finish from oxidizing.

The solder oxidized so that the marginal connection points became weaker until they were insufficient to provide the proper electrical signals. Pressing on the LCD momentarily created contact, but soon, the full display would fail in the field the worst possible scenario.

The only fix was to scrap the deficient calculators at a cost of millions. There are many lessons here, but one that stands out is to get expert advice if you do not know the area; almost everything is done for a reason.

Comments

Having worked at one time for the "phone company", we saw a similar thing happen with flex circuits and silver ink. After testing revealed oxidation, we soon switched over to carbon ink and the problems went away. Great article. It brought back many fond memories.
George Kopacz, PNY Technologies, USA

Submit A Comment


Comments are reviewed prior to posting. You must include your full name to have your comments posted. We will not post your email address.

Your Name


Your Company
Your E-mail


Your Country
Your Comments



Board Talk
How Effective Is Nano Coating On Stencils?
What Causes Board Delamination?
01005 Component Challenges and Bugs
Sticky Residue Under Low Clearance Parts
Soldering Relays Intrusively in Lead Free Process
Printing vs. Dispensing
Maximum Board Temperature During Tin-Lead
Is There a Spacing Spec for SMD Components?
MORE BOARD TALK
Ask the Experts
Recommended Fiducial Shape
HASL vs. Immersion Gold
Very Low Temp PCBs
Looking for Long-term Component Storage Options
Baking After Cleaning Hand Placed Parts
Conformal Coating Recommendation
Burned Chip Repair
BGA Component Grounding Problem
MORE ASK THE EXPERTS