Research
Electrical Testing of Passive Components
Electrochemical Methods to Measure Corrosion Potential of Flux Residue
Engineered Flux for Low Temperature Solders
Advanced Printing for Microelectronic Packaging
Assembly Reliability of TSOP/DFN PoP Stack Package
Solder Joint Embrittlement Mechanisms, Solutions and Standards
Through-Hole Rework for Challenging Components
Advances in Power Electronics
MORE RESEARCH
Latest Industry News
Hon Hai Unveils Three Electric Vehicle Models
Get Ready For The Next Generation Of Wearable Tech
Wistron to spend NT$10bn on facilities in Kaohsiung
Ghost Robotics CEO on Armed Robots for the U.S. Military
3 Ways to Get Comfortable With Changing Times
The prospect of Processing In Memory (PIM) in memory systems for AI applications
Biggest Tech Companies Now Building the Biggest Data Pipes
The Versatile Preform
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
Can Tape Residue Contaminate a Clean Tank?
Suggested Stencil Wipe Frequency?
Reflow Oven Zone Separation Challenges
When To Use Adhesive To Bond SMT Components
How To Clean a Vintage Circuit Board Assembly?
PCBA Inspection Concerns
When is it Time to Switch from Manual Assembly to Automation?
Keys for Moisture Sensitive Device Control
MORE BOARD TALK
Ask the Experts
Solder Paste Life on the Stencil
ESD and Humidification
Water Wash vs. No-clean
Dam & Fill vs. Conformal Coating
Solder Joint Blow Holes
Conformal Coating Bubbles
What Causes Component Rotation During Reflow?
Mixed Process Solder Joint Appearance, Smooth or Grainy?
MORE ASK THE EXPERTS