Fluid Jetting for Next Generation Packages - Nordson ASYMTEK 首页
Fluid Jetting for Next Generation Packages - Nordson ASYMTEK 首页
Fluid Jetting for Next Generation Packages - Nordson ASYMTEK 首页
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the DJ-2000 the best dots of Loctite SMA-<br />
3621 and of the Silver Paste occurred at 0.12<br />
mm stroke length and at 0.15 mm stroke<br />
length, respectively. These were both the<br />
shortest stroke lengths that could be achieved<br />
(at lower stroke length dots would no longer<br />
be dispensed). At lower stroke lengths the<br />
spring is compressed less, so there is less<br />
<strong>for</strong>ce slamming the needle back to its seat.<br />
Because of the consistency of the underfill (it<br />
is similar to syrup or honey), perhaps greater<br />
<strong>for</strong>ce is needed to separate a drop from the<br />
rest of the fluid. Even with 4 turns of preload<br />
the stroke length may need to be longer to<br />
get the required compression of the spring in<br />
order to jet a dot. The final parameter<br />
affecting the size of the dots was the<br />
temperature the fluid was heated to. It was<br />
found that by adjusting the temperature and<br />
leaving all other setting constant the dot size<br />
was not changed. However, when the fluid<br />
was heated to higher temperatures, the stroke<br />
length could be set lower be<strong>for</strong>e it began to<br />
clog. There<strong>for</strong>e, with more heat, the stroke<br />
length could be set lower, giving smaller<br />
dots, so temperature indirectly affected dot<br />
size. The other adjustable parameters did not<br />
seem to influence dot size quite as much. At<br />
higher preloads there is more <strong>for</strong>ce slamming<br />
the needle into the seat. This causes dots to<br />
be jetted at a higher velocity. With a higher<br />
velocity, the drops have greater momentum<br />
when they impact the surface and tend to<br />
spread out and flatten more. The amount of<br />
preload had to be balanced, so that there was<br />
enough <strong>for</strong>ce to eject a drop but not so much<br />
to flatten out the dot. However, the effect of<br />
this on the dot size was minimal (even at<br />
lower preloads the dots were still being<br />
ejected at a high velocity). Pressure was<br />
another parameter that had to be balanced.<br />
Pressure needed to be high enough to <strong>for</strong>ce<br />
fluid below and around the needle when it<br />
was raised, but also not so high that the<br />
pressure to back pressure difference was too<br />
large. With a pressure much greater than the<br />
backpressure, a greater amount of fluid was<br />
jetted with each drop. However, even when<br />
Pac Tech, Berlin, April 2002<br />
varying pressure between 10 and 50 psi, the<br />
influence of this effect on dot size was small<br />
compared to the influence of other<br />
parameters. The final adjustment made was<br />
the switch between the 4 and 5 mil nozzles.<br />
It was observed that the dots produced by<br />
either nozzle were comparable in size, and<br />
the 4-mil nozzle clogged more often than the<br />
5-mil nozzle. Because the nozzle size did not<br />
appear to affect dot size and have the<br />
clogging problems with the 4-mil nozzle, the<br />
5-mil nozzle was used <strong>for</strong> the rest of the<br />
testing. A final observation regarding the<br />
variability of dot size based on parameter<br />
settings is the potential benefit of this. The<br />
ability to adjust a few parameters and get<br />
dots which range in size from 12 mils<br />
diameter to greater than 30 mil in diameter,<br />
along with the ability to fire multiple dots in<br />
the same place (to get bigger dots) makes the<br />
DJ-2000 an extremely versatile piece of<br />
equipment.<br />
Recommendations:<br />
During the course of the testing several<br />
observations were made that could lead to<br />
improvements in the current DJ-2000 design.<br />
Currently the needle is stopped in its<br />
downward descent by slamming into the<br />
seat, which absorbs all of the <strong>for</strong>ce, and<br />
there<strong>for</strong>e must be constructed of carbide to<br />
withstand this wear. This extra cost (<strong>for</strong> the<br />
carbide parts) could be avoided as follows.<br />
By integrating an adjustable ring inside of<br />
the tube, and by adding a ridge on the shaft<br />
of the needle, the <strong>for</strong>ce could be transferred<br />
from the seat. The ring could be set so that<br />
the ridge on the needle comes to rest on the<br />
top of the ring. This would provide the<br />
stopping surface <strong>for</strong> the needle, rather than<br />
the seat. Because the contact area of this ring<br />
would be much greater than that of the seat,<br />
the <strong>for</strong>ce would be spread out more, and the<br />
component would not need to be made of<br />
carbide. The second proposed modification is<br />
to adjust the seat design to increase the<br />
backpressure on the fluid (the pressure<br />
pushing it up into the syringe). Having