I started off the day continuing my journey into a deeper cognizance of die bonding process. As we had seen yesterday, die bonding process involves die select, die pick-up, die transfer and die attach. The first two sub processes occur in the pick-up area, while the die attach sub process happens in the attach area. Die transfer takes place between the two areas. Naturally, these two areas need to be aligned to a common level. However, there is always a tolerance. The acceptable height difference between the areas is designated at 100µm. If the pick up area is higher than the attach area, machine speed will plummet due to prolonged travel time. On the other hand, if the attach area is higher than the pick up area, the propensity of the transfer arm to prang into the heater block cover will increase drastically.
As we all know, there are copious die sizes. Hence, different collets with the suitable size corresponding to the type of die handled are required. With that information in mind, I helped Miss Manggala to complete a subservient task, which was to check for any die sizes of package SOT363/SC88, from the intranet, which were not listed in a table of die dimensions that NXP Semiconductor is currently having. She will then need to make the purchase of those collets.
After completing the task, I proceeded to gain a deeper understanding of wire bonding process. First off, I stumbled upon what PHICOM really means. It is actually the acronym for Philips Computer. PHICOM machine is meant for wire bonding process. Generally, six steps are involved. I will provide the steps with the aid of the following pictures.
1) The capillary is moving from the spark to ball bond position. When the Free Air Ball (FAB) touches the die, which is also known as touchdown, the ball bonding process starts. Note that FAB is bonded on the die at elevated temperature, pressure and ultrasonic energy.
2) After bonding the ball, capillary makes the wire loop.
3) The capillary lands on the lead and wedge bonding process starts.
4) The capillary moves up. Next, wire-clamp is closed. The capillary moves further up to break the wire and thus from the tail (wedge).
5) As the wire reaches spark height, a tail is hanging under the capillary.
6) A spark forms a ball at the end of the wire. The wire-clamp opens and the air jet pulls the ball inside the capillary.
If you were heedful when reading the steps aforementioned, you would wonder, what is the purpose of ultrasonic energy? Actually, it serves as an avenue to wipe away oxides or undesirable contaminations on the contact area. Also, it helps to mature the bonding in combination with thermal energy. In other words, this insinuates that the ball bonding process can be carried out in a higher temperature. In addition, the presence of ultrasonic energy can soften the metal of Free Air Ball, thus rendering easier ball bonding process.
Apart from that, I had learnt that the difference between normal, reserve and trapezoid loop is the wire loop length. Besides, I got myself a fun fact too! Do you know that the melting point of gold is 1064°C? Oh! By the way, gold wire is the only material used for wire bonding.
I realized that the insipidity of this industrial training had returned when I was again ordered to update bonding diagrams. Now for SC88 package. Again, due to my fast execution, I was able to finish it by today.
30 April 2010
Mundane, sedentary nature of work is fast becoming an idiosyncratic aspect of my industrial training. Sporadic clandestine self permitted time off from facing the computer proved to be the only humdinger of my industrial training life. I started off the day doing again petty task, which is to tabulate the values I obtained from previous measurements into Microsoft Excel. As an overview, I tabulated ball diameter, ball height, wire pull, break point, ball shear as well as free air ball.
Next, try guessing what I was assigned to do. It was none other than the exasperating bonding diagrams!! I was given new package to update, namely SC70 and SC75. At the end of the day, I was able to complete them. I even had the luxury of calculating the bonding diagrams that I had done so far.
No comments:
Post a Comment