Page 116 - Wire Bonding in Microelectronics

W ir e Bond Testing 95

microscope. The shear tool extended downward from its clamp so that
it could operate in a deep package. A motor drive moved the test sam-
ple work holder to perform the shear test at a fixed rate of 0.2 mm/s
(8 mil/s). (This rate is not critical, since the rate of shear force applica-
tion does not affect the shear force value over the range of from 0.13 to
3.3 mm/s (5 to 130 mil/s [4-19]).
Currently, there are several commercial ball-shear testers avail-
able. The most sophisticated of these ∗ have automatic vertical position
finders, record data and failure modes, and can be interfaced with
computers and printers for final data analysis. The main mechanical
difference between modern ones and that of Fig. 4-11 is that Jellison
moved the stage and current ones move the shear tool. Of course,
current testers have greater position accuracy and measurement pre-
cision, are semiautomated, and much easier to use.
4.3.3 A Manual Shear Probe As an Aid in Setting Up
Ball Bonder (For Laboratory Use)
It is always desirable to have a quantitative, precision shear tester.
However, if such is not available, a simple substitute can be made
that will give information, that, while not quantitative, will neverthe-
less allow one to quickly set up ball-bonding machine parameters
and qualitatively evaluate bonds for laboratory or other nonproduc-
tion purposes.
The simplest and most readily available tool for manually push-
ing off large (non-fine pitch) ball bonds is the blunted end of one tine
of a tweezer, and production personnel have used such for this pur-
pose for years [4-18]. However, tweezers are relatively awkward to

use, particularly if the ball is strongly welded. A simple manual shear
probe has been designed for this purpose [4-11].Figure 4-12, detail A,

is a drawing of a probe tip that is appropriate for use on balls made
from wire of up to 33 µm (∼1.3 mil) in diameter and of course pitch.
The tip can be made by a machinist or a precision tooling company.
However, a reasonably satisfactory one can be made in a few minutes
using the smallest blade from a standard jeweler’s screwdriver set.
This blade, while still in the jeweler’s screwdriver set as a holder, can
be manually narrowed and thinned on very fine emery paper to the
approximate dimensions of Fig. 4-12, detail A. (Note the use of a manual
shear probe is not practical for typical ball bonds on pads having pitches
finer than ∼100 mm.)
In use, the sample is placed on a holder at a height such that the
probe, when held like a pencil, will approach the surface at an angle
of about 20 to 25°. This matches the angle on the tip of the tool. The ball

∗ Some manufactures are Dage Precision Industries Inc., UK, Aylesbury,
Buckinghamshire, HP19 8RG, and Royce Instruments Inc., 500 Gateway Drive
Napa CA 94558. Both have sales/service offices worldwide.