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It’s me PRINCE. I just wanna know the difference between the gorilla glass and soda lime glass. Tell me which one is suitable for touch mobile phone’s smart shield?

Hey Prince:

And I thought everyone in the touch screen business had read my white paper on glass! Let me summarize the salient points, even though none of us are worldly enough to know what a “smart shield” is.

First, if your purpose is to protect the touch screen, glass is a better and more long lasting option than plastic. Touch performance is better through glass, and its non-scratch characteristics exceed all but the most exotic (read expensive) plastics….it is also clearer and thus easier to read information on the display.

But you are asking Touch Guy to enter the battle of which is best…Gorilla (Corning’s trade name for AAS glass [read the white paper]) or soda-lime glass in this application. In the beginning, shattered-glass-there were a lot of problems with the touch panels breaking when the smart phone was dropped (good business for Touch Guy), so the top layer, called cover glass or cover lens, was chemically strengthened, which helped reduce breaking. Chemically strengthened glass is made by exchanging sodium ions for potassium ions, the latter being bigger. After this process the top surface is compressed and the glass under surface remains under tension, which makes the glass much more difficult to break. Gorilla glass and plain-old-soda lime glass have pretty much the same break resistance after the chemically strengthening process.

However, AAS glass is more porous, so when it is chemically strengthened, the potassium ions go deeper into the surface of the glass. If your habit is to put your smartphone in your pocket with your keys and spare change, and if your active life-style causes the keys to scratch the glass, the surface compression ions will be compromised first in soda lime because they are not as deep.

The person with the pocketful of keys and smartphones will need a lot more 10,000-step-days before his Gorilla cover glass will break when dropped (her smart phone is probably not in her pocket, so you may need a “his” and “her” version of whatever smart shield is).

Now, in the more than you wanted to know about the matter category…all glass is vulnerable to cracking when it gets hit on the edge…and the most vulnerable is glass that is not seamed (smooth edge) before it is chemically strengthened. In the purely rumor category, the iPhone 5 was the first to use Gorilla glass, and initial comments were that it was breaking more than the-plain-old-soda-lime touch panels. The purely rumor explanation was that the initial phone design had more access to the edge of the cover glass, so it was easier to whack and therefore break….welcome the law of unintended consequences. So you will want to step in your smart shield a little to protect its edge.

So there you have it. Quite possibly, after all that you may have still not got the answer you were looking for even though I hope you learned something. I can definitely appreciate the repair market for smartphones. Of course, Touch Guy’s new all plastic molded touch screens will not break or scratch – so perhaps many devices will not need this “smart shield” in the future.

Keep Calm and Touch On,
Touch Guy.

“Hey Touch Guy, why can’t the military use projected capacitive?” – Ready, aim, fire!

Whoa, simple question – complex answer.

First, the “military” does use projected capacitive (p-cap for short), and purchases a huge number of iPads and iPhones.  But I think your question is, “Can the military use p-cap in a battlefield environment.”  Yes, there are problems that have slowed the introduction of p-cap.  Here are a few that need to be addressed, and are being overcome.

Most of the armed forces are very careful about generating EMI that could be detected by the bad-guys.  P-cap, you will recall, works by having a human drain capacitance from the touch screen at the touch point.  For multi-touch, that means lots of small fields are created on the TouchGuy_Basicsurface of the touch screen.  The fields are quite small, and inconsequential compared to the EMI from radios that are in most devices, but they are still there.  TI has been able to tune the frequency to meet

EMI is a general problem, but it’s not alone in the obstacles p-cap must overcome.  The Navy and Coast Guard, not surprisingly, want rain and sea-water immunity.  Solutions have been developed in the electronics to compensate for tap and rain water.  But sea water, because it is more conductive, is a more difficult matter because it spreads a conductive film across the touch area, and when a finger is touched to the screen the capacitance is drained from lots of points which confused the touch electronics.  TI has developed a new total immunity sensor that works both mechanically and electrically to provide immunity to sea water.

Both the Army and Air Force require gloved finger operation.  For most flight applications, the gloves are thin-enough that p-cap is a great choice.  However, for some Army applications, the gloves are bigger and thicker and an accurate touch is more difficult…Touch Guy does not think this is a real issue because if the gloves are so big and bulky, how can you touch a small point anyway?

Impact, and the resulting breakage, is another issue, as most p-cap touch screens are made from glass.  There is also a weight issue in using glass.  The obvious solution is to make the p-cap sensor completely out of plastic or some form of acrylic substrate, however, plastic can scratch in some environments. Technology to the rescue, there are new transparent hard-coats for plastics that can approach the scratch resistance of glass.

In conclusion, Touch Guy believes the real roadblock preventing the introduction of p-cap into the battlefield isn’t the touch sensors themselves, but the lack of new programs that would make use of the latest and greatest touch technology has to offer.

Remember, I come in peace! – Touch Guy

My engineers claim gestures on multi-touch resistive do not work nearly as well as they do on projected capacitive (PCT) used in a variety of consumer devices, like the iPhone – why is this? Have there been any recent breakthroughs with resistive multi-touch? I would appreciate any new input on this subject.

Hi Alex:

When you are comparing iPhone/iPad projected capacitive (also called PCT or P-Cap) to any other (even identical) projected capacitive sensors, you may not find the performance to be as good as Apple ’s product.  How can this be?  It is because Apple has had a really big head-start (as in years).  You and yours are playing catch-up, and it will take a while for you to integrate the prior art (yes, Apple did not invent multi-touch) with the new, to achieve the same thing.

Here is a good example:  Using a multi-touch demo, you can use the pinch gesture to make the picture really small….so small, that you will not be able to “catch” the corners and expand it…it will stay really small untilTouchGuy_Basic you reset the program.  Apple has anticipated the picture getting too small, so their software will accept nearby fingers and “guess” that the user wants to expand that photo, and it will.  There is a lot of anticipation in the iXX software that makes it better than your stuff.  Touch Guy is a hardware person, so you can guess that he will point the blame finger at the software folks.

Now to your original question…  MARS is different only in the pressure required to enable the gestures.  Otherwise, the gestures should be the same and the performance the same as projected capacitive and better, of course, with input from pens and pencils.  Keyboard entry is noticeably better with sure-footed MARS than with projected capacitive, which seems to often “guess” wrong at which key you wanted (auto correct to the rescue).

For more info on multi-touch, check out Touch International’s Putting the ‘Touch’ in Multi-Touch White Paper.

Touch Guy