Techcon-Piezo-Jet-Valve-Dispensing - 第3页

Jet valv es—both the older pneumatic jet technology and the new er piez o jet technology—gain a signifi - cant speed advantage primarily b y eliminating the Z axis of mo vement. T he height sensing and re-po - sitioning …

If your operation needs

the ultimate in speed and

precision, the cutting edge

of dispensing technology

may be right for you.

By Can La, Product Manager, Techcon

Selecting the automated dispensing technology that

is the best fit for a specific application from the half

dozen or so familiar technologies available—such as

the auger valve, progressive cavity pump, time pres-

sure valve or pneumatic jet valve—is not a consid-

eration to be made lightly. For most operations, the

consequent match is adequate, and attributes such as

throughput and quality are well suited to the applica-

tion on an ongoing basis. For others, however, such as

medium to high volume mobile device, LED, consum-

er electronic and medical device assemblers, there is a

constant drive for the ever higher yields that can drive

improved profitability, and for an advanced dispens-

ing technology that can better help them achieve it.

For these users, there is a relatively new technology

that can increase dispensing rates for adhesives and

other fluids by some 20x or more—at rates, for com-

parison purposes, as fast as 1500 Hz continuously

with up to 2000 Hz maximum burst. It’s called the

Piezo Actuated Jet Dispensing Valve, and it dispenses

at about twice the speed of even the pneumatic jet

valve.

Operators are also often amazed at the impressive

placement precision and small and neat dot sizes

generated by a piezo jet valve, especially considering

that a) it is moving so fast, and b), the material is be-

ing shot and not being physically placed, as would be

the case with most dispensing solutions that rely on

actual contact with the substrate. Using sophisticated

controllers, shot sizes can be achieved as small as .5

nanoliter, with outstanding consistency and repeat-

ability. This precision also makes the piezo jet suitable

for some other niche applications where speed is less

of a factor, but where operators have a challenging

time achieving the desired dispensing of ultra-small

dots or ultra-thin lines consistently over time.

2X FASTER

than pneumatic

jet solutions

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.