ASM_Guide To Adhesive Dot Dispensing_Stinger_en_0321_online.pdf - 第55页

2 STINGER, A GUIDE TO ADHESIVE DOT DISPENSING 2.6 BEST WORKING PRACTICES GUIDE TO ADHESIVE DOT DISPENSING STINGER 03/2021 55 Warp occurs in the Y direction due to board clamps pulling the product down over the tooling; f…

2 STINGER, A GUIDE TO ADHESIVE DOT DISPENSING

2.6 BEST WORKING PRACTICES

54 GUIDE TO ADHESIVE DOT DISPENSING STINGER 03/2021

2.6.2 The Adhesive

Many factors have an affect upon the performance of the adhesive and its use in dispensing applic-

ations.

The adhesive is stored in a refrigerator prior to being used. These cooler conditions alter the nor-

mal viscosity of the material and it may need to be brought to ambient temperature, over a period

of time, before use. The exact heat ramp figures vary for different adhesive types; check manufac-

turer’s data sheets for details.

The ambient conditions of the factory may also influence the success or not, of the ability to dis-

pense adhesives. If the humidity is too high, this may introduce moisture absorption which in-turn

degrades adhesion.

Voids can be formed due to water absorption; air entrapment; and solvent loss. Voids not only cre-

ate weak spots they can, if the condition is left long enough, cause the adhesive to dry out.

Each nozzle has a process window; there is a minimum and maximum dot each nozzle size can

create. While it’s possible to dispense more adhesive through the nozzle, this may lead to other

process problems. It is better to dispense several dots next to each other than it is to dispense one

large dot.

In the system, Stinger utilises a fully enclosed delivery system. Product changeover is a simple pro-

cedure, which in general takes little more than a minute to complete. The assembly is replaced as

a single unit - the nozzle, syringe, auger and feed path. In this way many of the problems associ-

ated with breaking the system apart for cleaning are eliminated.

A useful tip is to program sacrificial sites (1 or 2) before the production deposit sites; these sacrifi-

cial sites allow the system to ‘work’ the adhesive, before laying down the crucial production sites -

this gives greater stability at the production sites.

2.6.3 The System

Ensure that all calibrations are carried out and that they are repeated if:

●

The feed path has been changed

●

The nozzle has been changed

●

The current product has significantly different properties to the previous product, i.e. board ri-

gidity, thickness and warp

●

During calibration there is any movement of the product

●

Any of the calibrations have been adjusted

Calibration should be carried out under the same conditions and with the same tooling as that used

for production. The calibration board must be typical for production.

Z-Axis idle position is the height that Stinger moves between dispensing. The height should be set

to ensure the nozzle does not drag adhesive strings during camera axis moves. A higher idle

height ensures paste drag does not occur and promotes ‘snap off’; setting it too high adds a small

amount to the cycle time.

Offset calibration is used to calibrate the difference between the nozzle and the laser; it is a once

only calibration and should not be used to move dispense dot locations.

The laser retains measurement information from the previously measured site. It is recommended

that at least the first site in the process is measured. This ensures that product-to-product vari-

ations are compensated for.

2 STINGER, A GUIDE TO ADHESIVE DOT DISPENSING

2.6 BEST WORKING PRACTICES

GUIDE TO ADHESIVE DOT DISPENSING STINGER 03/2021 55

Warp occurs in the Y direction due to board clamps pulling the product down over the tooling; for

this reason it is recommended that any large changes in Y site coordinates is accompanied by an

initial laser measure.

2 STINGER, A GUIDE TO ADHESIVE DOT DISPENSING

2.7 ERROR RECOVERY

56 GUIDE TO ADHESIVE DOT DISPENSING STINGER 03/2021

2.7 ERROR RECOVERY

Symptom Possible Cause Solution

Product surface being pushed

down during dispense

Contact height incorrectly calib-

rated

Re-calibrate Contact Height.

Ensure that the product is not

deflected and that the cali-

bration board is representative

of the production boards

Inconsistent deposit Product warpage is present but

laser correction is not being

used

Switch on laser measurement

for deposit sites

Inconsistent deposit Product warpage is greater

than +\- 1mm

Use vacuum tooling or a

product that is within tolerance

Dispense motor is turning, but

no material is being dispensed

System needs purging, pos-

sible drying of adhesive

Purge the system, if the condi-

tion persists change the dis-

pense feed path assembly

Dispense motor not turning Dispense motor belt tension too

tight

Reduce belt tension

Dispense motor timed out Dispense motor stalled due to

adhesive drying out and form-

ing a blockage

Discard and replace the dis-

pense feed path assembly

No feed Adhesive dried in feed path Discard and replace the dis-

pense feed path assembly

Inconsistent delivery, particu-

larly during a purge

No air Ensure that the syringe is being

pressurised (pulsed) during dis-

pense and purge routines

Dispense site outside of board

area error

Site location incorrectly pro-

grammed

Continue, and ignore the warn-

ing. Skip the offending site or

Stop the print run, and re pro-

gramme the site location for the

correct location; or remove the

site altogether

Auto-Calibrate Fails Calibrate X and Y location

incorrectly set

Locate the calibration point so

that neither the laser nor the

nozzle are over board cut-outs

Auto-Calibrate Fails Vision height or other variable

has been changed

Perform a manual calibrate to

reset the laser range