Development of a Oxygen Sensor for Marine ... - DTU Nanotech

6.2. THE FLEX PRINT 53
The reason behind letting the conducting glue dry slowly in step 3, rather
than putting it in the oven right away, was that tests showed a lack of connection
if the glue hadn’t dried properly first.
Also it should be noted that while the solution with the conducting glue
does work, it is not the most optimal solution, as the yield on working sensors
with this solution is discouragingly low.
6.2 The flex print
There was also another problem with the wirebonds, or rather the flex print,
even if the wire had been successfully attached to both the output electrodes
and the flex print. After taking the packaged device out of the oven, the flex
print appeared to bend upwards, despite the glue. This had the side effect
of making the thread snap off at one of the ends. Hence cutting off the connection
between the chip and the flex print. The reason for this appears to
be that the flex print used, isn’t suitable for use with temperatures over 80 C.
Figure 6.6: Picture from a chip, where conducting glue have been used to
form the connection between chip and flex print, as can be seen
the flex print have bend and caused the connection to break.
So in order to solve this, a way to keep the wire attached or to prevent
the flex print from bending had to be found.