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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…

2 STINGER, A GUIDE TO ADHESIVE DOT DISPENSING

2.6 BEST WORKING PRACTICES

GUIDE TO ADHESIVE DOT DISPENSING STINGER 03/2021 53

2.6 BEST WORKING PRACTICES

Developing, maintaining and managing best working practices is key to obtaining high quality

throughput.

2.6.1 The Product

The product needs to be kept clean, de-greased and dust free to ensure that the adhesive is able

to adhere to its surface and that of the placed component.

It should also have a good surface flatness and be well supported with tooling underneath. Vacuum

tooling offers excellent support and helps to eliminate board warpage. Any surface protection lay-

ers or masks should be smooth and flat.

The diagram opposite shows how it is able to ‘track’ the contour of the product surface and main-

tain the dispense gap which has been set.

The contact height is set first, this is the datum point for setting the Z-Axis parameters including idle

height and dispense gap. When the dispense gap has been set up, this height is maintained des-

pite board warpage being present.

A Contact Height Setting – The Z-

Axis contact position, for any

product, is within +/-1mm

of the

calibrated contact position

3 Contact Height

B Dispense Gap 4 Dispense Gap

1 Dispense Nozzle 5 Dispense Gap Maintained Across

the Product

2 Product

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

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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.