Manual

7-14 Advanced Programming
Underfill Patterns
One application that typically uses the multipass feature is underfill. There are several types of line
patterns used for underfill applications. Two common types are L-shaped and U-shaped patterns as
shown in Figure 7-10. Variations of these types of underfill patterns are used as well. These patterns and
processes are designed to assure complete underfilling without excess and to prevent voids in the underfill.
Item Description
1 Flip Chip
2 First Pass of L-shaped Pattern
3 Second Pass of L-shaped Pattern
4 U-shaped Pattern
5 First Underfill Pass
6 Second Underfill Pass
7 U-shaped Seal Pass
Figure 7-10 Underfill Patterns
Order of Pattern Placement and Timers
The order that the patterns are dispensed is an important part of optimizing the whole workpiece program.
For instance, in a U-shaped pattern, as shown in Figure 7-10, the first underfill line is dispensed at all
pattern locations on the workpiece. Then, the second underfill line is dispensed at all pattern locations.
Finally, the U-shaped seal pass is dispensed at all pattern locations. Timers are set for each of these steps
using the Reset Multipass Timer and Await Multipass Timer commands. This technique is demonstrated
in the exercises later in this section.
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