11-14 May 2010

11 May 2010

Today, I gained a better understanding of the operation as well as errors akin to ADAT and PHICOM machines. First off, I observed how a technician attended to “Post Bond Total Skip Count Exceeded” error on an ADAT machine. Initial comprehension was that presence of tilted dies were detected, which rendered the PRS image darker than usual. The technician once thought it was just sporadic occurrence; however, subsequent series of same errors faulted his initial judgment. He then discovered that the push up needle was rickety and promptly replaced it with a new one. Push up needle serves the purpose of pushing up the designated die to be picked up by the collet.

Next, still within the vicinity of ADAT machines, I came across “Touchdown Push Up Too Soon” error. This means that the push up needle elevated the die too soon for the collet to pick up. The operator attended the problem by changing the process delay value.

Mr. Leong provided me with several additions to my knowledge of ADAT as well as die bonding process. He taught me that there the first die attach machine was invented by the Germans. Predictably, it was slow. Then, we have ADAT1, ADAT2 and ADAT3. For ADAT2, there are 3 different types: ADAT2 12k, ADAT2 14k, ADAT2 18k, with the last type being the fastest among the three. So, the notation of 12k, 14k and 18k simply impregnates the idea of different speed. Apart from that, Mr. Leong also talked about what SOT and SOD mean. SOT is the acronym for Small Outline Transistor, while SOD means Small Outline Diode. Furthermore, the helpful Mr. Leong told me that RF (Radio Frequency) products are relatively costlier as more convoluted process is implicated in which wafer back coat is required. Wafer back coating is similar to glue bonding.

Next on the agenda are errors associated with PHICOM wire bonding machines. When one encounters “Total Skipcount Exceeded” error, it probably indicates that the predetermined allowable number of units that are devoid of dies or “Total Skip Setting” value was reached or exceeded. There is always a “Skip Counter” indicator beside the “Total Skip Setting” to tell us about how many units have been skipped by the machine. Another setting worthy of mentioning is “Sequential Skip Setting” which is similar to “Total Skip Setting” except that it indicates the number of acceptable consecutive defective units to be skipped. Besides that, when the error “Spark Not Completed” pops out, it means that spark is not provided for wire bonding process, culminating in the failure to form Free Air Ball (FAB).

In addition, I also tried my hands on die shear. Previously, I had been performing ball shear. After several runs with ball shear, I can deem myself as an expert in ball shear. However, the same cannot be said to die shear. The first thought that came to mind was that it would just be a piece of cake. It turned out to be an exhilarating experience though it was tremendously difficult. In the process, I managed to obliterate many dies. Poor dies, rest in peace…

12 May 2010

Today was really a humdinger as I was assigned something totally different and challenging. Before I go into details of what I was asked to do, Miss June briefed me about the upcoming production of a new product which is based on upbent lead frames, which have the major as well as minor bond pads elevated slightly. Customarily, lead frames are completely flat. Miss June’s briefing was rather vague and convoluted which culminated in me enveloping in a mist of uncertainty and questions.

Uncertainty notwithstanding, after being provided with relevant information, I proceeded to calculate the length of that bent portion. Subsequently, with that aforementioned value in mind, I calculated the angle of bending. After obtaining those theoretical values, I went into the assembly line where I performed several measurements to acquire some practical values, in order to vindicate my theoretical findings. Fortunately, the values obtained theoretically and practically were coterminous at worst and exactly the same at best.

Next, I moved on to calculate the angle of R35 capillary tip. Before I could attain that, I did some concise research on the parts of the R35 wire bonding capillary, and understanding the parameters or dimensions involved. Based on the Outer Diameter (OD), Length (L), Cone Angle (CA), I was able to determine the outer angle of R35 capillary tip as well as the cone vertical height.

Moving on, I evaluated the remaining space available when a flat lead frame is to be used upbent. With that in mind, and information regarding die size, I also determined the final remaining space available after the die is attached to the bond pad. After that, I went into the assembly line again to measure the major and minor bond pad length.

13 May 2010

I continued where I left off yesterday, performing measurements of major as well as minor flags length. I was able to finish the measurements of three distinct lead frames, which are designated for SOT343F, SOT343R2 and SOT363F. Also, I finished measuring the bending angle and the bending base length of SOT343F and SOT363F lead frames. The same cannot be performed on SOT343R2 lead frames as this type of lead frame is not upbent. After lunch, I continued my unique relationship with the measurement device as I was assigned to perform 360 measurements in order to determine ADAT and PHICOM consistency. All of these are part of the challenging assignment given to me yesterday.

14 May 2010

I tabulated all the data I acquired in the past two days. For the 360 measurements involving horizontal and vertical distances from my designated reference point on the major flag to the die as well as from a designated reference point on the minor lead to the wedge bond, I also calculated the hypotenuse distance in order to determine the consistency of ADAT and PHICOM machines. For the machines to be regarded as consistent, the standard deviation is to be less than 10µm, which is rightly so for both ADAT as well as PHICOM machine.

While waiting for Miss June to assign me with further tasks, I spent my time taking images of die pushed units. Similar to die shear units, the die on each individual unit is removed by force. For die shear products, the die is removed by machine, however, for die push units; the die is removed by tweezers held by human fingers.

After lunch, after lucid explanations from Miss June, I began the intriguing calculation of the possibility of capillary hitting the die. To show this, I needed to calculate the distance between the capillary and the die during wire bonding process. I considered the ideal case, where the die is situated at the middle of the major flag, as well as the worst case scenario, in which the die is displaced for 20µm. This maximum displacement value is calculated by evaluating the process capability index of 4σ.

I will upload all the photos pertaining to the calculations that I had done when I gain internet access again. For your information, my home is without internet for one month. I know, it is agonizing. That is why I could only update my blog so sporadically