June, 2016 Continued from previous page
minum coupon using 2 mil aluminum wire. The wedge bonder’s power parameters were varied
www.us-
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was observed at power setting of 50 for the plasma- treated pads. More significant, however, is that there were 95 percent bond breaks with only 5 per- cent lifts for the plasma-treated pads versus 50 percent breaks and 50 percent lifts for the untreat- ed substrates. As today’s market demands more compact
Wedge bonding performance on plasma-treated and untreated substrates at low and high bonding parameters.
through a chosen range, producing non-sticks during bonding at lowest power settings and 100 percent breaks during pull testing at high power settings. Each wedge bond was created using deformation cut-off control. After plasma, pull strengths are
higher at lower power settings as opposed to the untreated substrate. Also, the pull strengths between untreated and plasma-treated pads converge at higher bonding powers. This shows that the higher bonding power overwhelms the benefits of the plasma. At very low bonder power settings, there is a substantial reduc- tion in non-sticks after plasma treat- ment, when compared with untreated bond pads. Essentially, there are 100 percent non-sticks for the untreated pads versus less than 10 percent for the plasma-treated pads. Further - more, the data also shows a signifi- cant increase in bond breaks versus lifts for the plasma treated sub- strates. In another view, data was plot-
ted to highlight bond performance as a function of low and high power parameter settings, comparing plas- ma-treated and untreated surfaces. Low bonding parameters were de - fined as the lowest power settings that showed zero non-sticks during bonding. High bonding parameters were defined as the lowest power set- tings that showed zero lifts during pull testing. The data shows that plasma-treated substrates and low power settings completely outper- form untreated substrates. Zero non- sticks were encountered after plasma versus 20 percent non-sticks for the untreated substrate. Plasma treated pads had 70 percent wire breaks ver- sus zero wire breaks for the untreat- ed pads (100 percent wire lifts). Also, there was a 25 percent increase in overall bond strength after plasma. At high power settings, both
plasma and untreated substrates produce zero non-sticks and overall pull strengths are similar; plasma treated pads show only a slightly higher average pull force. The main difference between untreated and plasma-treated pads at higher power is that untreated pads result in 90 percent bond lifts versus zero bond lifts for plasma treated pads. When the wire bonding trials
were extended to bonding on copper, similar results were obtained. Again, each wedge bond was created using deformation cut-off control. In these experiments, a mid-range bonding power setting produced the best result for the plasma treated pads. A small increase in overall pull force
electronic packages with increased functionality, die need to be thinner and stacked. Bonding to overhangs on thin, stacked die can result in die crack, loop damage and poor bump formation due to “bouncing.” Optimizing the wire bonding process is often required to minimize and eliminate these problems. Most critical are the power parameters (ultrasonic and capillary force). Plasma treatment of bond pads prior to wire bonding dramatically increases wedge bonding performance. The full potential of plasma treatment, however, can only be realized if it is accompanied by the correct bon- der power parameters. This is particularly evident
Page 61
Wire pull strengths on copper plotted as a function of bonder power setting.
at low power bonding parameters, where a dra- matic reduction in non-sticks during bonding, and lifts during pull testing, is observed. Contact: PVA TePla America, Inc.,
251 Corporate Terrace, Corona, CA 92879 % 951-371-2500 fax: 951-371-9792 Web:
www.pvateplaamerica.com r
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