Techcon-Piezo-Jet-Valve-Dispensing - 第4页

In a piez o jet valv e cycle, the fluid s tarts up inside the valv e, held between the tappet (pis ton) and the nozzle . The electronic pie zo crys tal oscillates up and down a t a high rate of speed, gener ating kinetic…

Jet valves—both the older pneumatic jet technology

and the newer piezo jet technology—gain a signifi-

cant speed advantage primarily by eliminating the

Z axis of movement. The height sensing and re-po-

sitioning and the up and down motion that is nec-

essary for contact-based valves such as progressive

pump and auger valve technologies—with the needle

moving down to touch the substrate to dispense the

fluid and then pull back up—while reasonably fast by

most criteria, account for a high percentage of the

required dispensing time. Contact-less jet dispens-

ing, by contrast, shoots the material accurately from

a fixed location above the substrate, shot after shot.

This enables the pneumatic jet valve to reclaim this

excess motion time and dispense at speeds some 10x

faster than contact-based valves.

However, while the pneumatic jet valve technology

leaves the speed enhancement at “only” 1000%, the

piezo jet valve ups the ante considerably. In these de-

vices, rather than relying upon air pressure, a piezo-

electric actuator converts an electrical signal into a

highly precise motion that dispenses the material

in the desired pattern far faster than a mechanical

pneumatic based solution, which must open and

close and reset, a process which ex-

pends some 20 extra millisec-

onds each time. In this

way, speeds up

to 2000%

faster than contact-based solutions—2x faster than

pneumatic jet solutions—can be achieved. For speed

sensitive, high volume, high throughput applications,

the increase in yield can be extraordinary—and highly

profitable.

Further, the ability of the piezo technology to deliver

the smallest dots or lines—with micro shots as small

as .5 nanoliters—is hard to beat. As is the accuracy

and repeatability of each and every dispense.

Another huge advantage of the piezo jet technology

is its ability to deliver this up to 1500 Hz speed even to

those operations involved with the production of sub-

strates with irregular heights, or those where hard-

er-to-access “nooks and crannies” must be reached.

Since the fluid is shot rather than dropped, nozzles

can be more readily angled to reach the exact point

where material is required. Further, since the nozzle

doesn’t need to drop down on the item, products

with irregular protrusions such as a motherboard with

high spots won’t be damaged as they might be when

utilizing a contact-based valve that must come down

close to the substrate, eliminating a common source

of damage, waste and downtime.

Rather than relying upon air

pressure, a piezo electric actuator

converts an electrical signal into a

highly precise motion

Piezo Jet Technology

where the speed comes from

In a piezo jet valve cycle, the fluid starts up inside the valve, held between the tappet (piston) and the

nozzle. The electronic piezo crystal oscillates up and down at a high rate of speed, generating kinetic

energy that forces the fluid to shoot out under carefully controlled pressure to form a perfect bead of

material at the target location.

How It Works

A complete, five step piezo jetting cycle consists of:

• Rising Time - Total time for the tappet to move to open position

• Open time - Total time the valve stays opened

• Falling time - Total time for the tappet to move to closed position

• Needle lift - is the stroke length, based on the viscosity of the materal.

• Delay time - Time the valve stays closed, waiting for the next cycle

All of these steps can occur, repeated over and over again, up to 1500 times per second continuously, with that

number an objective basis for comparison with other dispensing methods being considered. Under real world

conditions, the number of drops dispensed per second will be impacted by factors such as desired shot size,

the viscosity of the material, and the speed of the horizontal movement of the substrates being assembled.

In use, as noted, contact-less piezo jet valves can typically dispense about 20x faster than any contact valve.

When considering upgrading to the power of a piezo

jet valve dispensing system, a vital point to be aware

of is that the phrase “jet valve” can refer to both the

older pneumatic jet valve as well as the newer piezo

crystal driven jet valve technology. While both tech-

nologies, as noted, are significantly faster than familiar

contact dispensing options such as the auger valve

or progressive cavity pump, the newer piezo version

of the jet valve ups the ante considerably, and as not-

ed can deliver some 2x the speed of the incumbent

pneumatic version. Nevertheless, since for so many

years “jet valve” referred only to “pneumatic jet valve,”

many people still use the terms interchangeably, and,

indeed, many potential users and even valve manu-

facturers are relatively unfamiliar with the piezo jet

valve or have not yet had the impressive experience

of seeing it in action. In other words, it behooves the

buyer to specifically refer to “piezo” in all discussions

to ensure that everyone is on the same page.

Currently several manufacturers provide piezo jet

valve dispensing solutions, and, as one would expect,

a number of aspects of their design as related to both

the valve itself and the related controller can differ

significantly.

For example, a key issue to consider is the relative

ease of identifying the right “recipe,” the combination

of parameters to ensure correct placement and the

correct amount of material. Piezo valves gain much of

their small dot consistency through not only making

use of tiny aperture nozzles but also by providing

the flexibility to fine-tune both material pressure

and jetting pressure. Once the correct parameters

are determined, the valve is extremely accurate and

consistent in maintaining them, but getting to that

point can and often does take some trial and error.

Key in reducing the challenge are the capabilities

of the controller provided, as well as any assistance

that might be available from the manufacturer. As to

the latter, some manufacturers might just look at an

MSDS and render an opinion. Others will offer some

level of hands-on testing of your material in their labs

to assure efficacy. Further, they might be willing to

use the knowledge gained to help you more quickly

fine tune the parameters back in your operation. It

pays to inquire before the sale.

Even more impactfully, the user interface of the con-

troller can make a huge difference in the relative ease

in determining the proper parameters, and therefore

the level of potential wasted product or loss of pro-

ductive uptime during initial product set up.

Techcon TS9800 Series Jet Valve

Highly repeatable and precise

dispensing for outstanding

process control

Ease of use, size of footprint

and other purchasing considerations