3rd week

This week, I was assigned to do a summary on time mapping of the exposed pad using Microsoft Excel. In the summary, some important points such as date, machines number, team, leadframe supplier were to be highlighted so that it could be noticed easily. The summary should be in a simple and presentable form. The reader will be easy to understand what the summary was.

On the other hand,I was given a task to do a simulation of DA ESEC report in order to find the root cause of the exposed pad. The picture shows a tilted leadframe on the middle.




The leadframe was sent to WB. One of the tilted leadframe can be auto aligned by the WB machine but the other needed manual alignment to go through the WB process. After that, the leadframe was sent for mold process. Unfortunately, there was no exposed pad found. This might not be the root cause of the exposed pad.

A 'why why analysis' is used to find the root cause of the exposed pad. First, list out all the possibilities that might cause exposed pad. Then narrow them down by carried out some simulation. After that, eliminate out all the non possible causes and then do a further investigation o the remaining possibilities.

Besides that, I was to monitored the DA ESEC machines for further confirmation if it was to cause the exposed pad problem. The time mapping summary was also updated accordingly.

There was no tilted leadframe detected in four days, but monitoring still going on. A mold engineer told me that if it was for exposed pad to happened in mold process, all the wires in the unit will be broken. This was another helpful information.

On the fifth day, another exposed pad case was discovered. Still, the DA ESEC machine did not have tilted leadframe cases. This showed that the root cause for DA process is low. A WB simulation was carried today, but in the end, no exposed pad was discovered. Other possibilities were to be looked on to find the root cause.

2nd Week

Week 2:

This is the second week of industrial training in Numonyx. This week, I was given an assignment by my supervisor. The task is to find out the causes of ‘Exposed Pad’ of the devices. Each device will go through mold process but some minor amount of device will have the problem of exposing its leadframe at the bottom of the device. This is a critical threat, if one of this device escape to the customers, the company will surely suffer its consequences.
Basically, there are many factors that can cause ‘Exposed Pad’. The causes are such as material quality, machine problems, human carelessness, handling and many more. A ‘4M’ & ‘4w 1H’ method is used to analyse the problem. ‘4M’ is Material, Man, Machine and Method. ‘4w 1H’ is who, what, where, when and how. So, I was given some data on exposed pad cases and to summarize and sort them.
Actually, ‘Exposed Pad’ is manily caused by the downset of the leadframe. Downset is caused by the bending of degate. Due to this problem, it will cause ‘exposed pad ‘ in the molding process.
Besides that, I also need to monitor all the machines involved in ‘Exposed Pad’ in order to find out the tendacy of causing leadframe downset. The machines are such as DA, WB, Molding machines. These three processes will have a higher chances for leadframe downset to happen because each process involved transporting.

Industrial training (1st week)

Day1

Today is my first day of industrial training in Numonyx. Firstly, I was brought to the human resource department to have a short briefing. Numonyx is a semiconductor manufacturing company, its main products are NAND, NOR memory which are widely used in the cellular phone industries and also electronis devices. Numonyx is formed by ST Microelectronics and also Intel. Both of these companies merged their flash memory department to create Numonyx. Eventually, Numonyx is currently own by Micron, one of the biggest memory manufacturer world wide.

I was then assigned to ‘K2’ also known as the assembly department. My supervisor is Miss Tan Mei Yan, an experienced assembly engineer in Numonyx. She is very kind and willing to teach me. Today I was given some power point slides on the basics of chip manufacturing process flow. I was told to get a rough idea of what is going on before going for a line tour. All the staffs here are very friendly and helpful, but unfortunately they are very very busy. This is how an engineer works!!!

Day2

Today, I went for a line tour escorted by my supervisor. She explained to me each of the process flow of how a chip is made. There are 2 types of devices, which are TSOP and SO8L. The processes are quite similiar, which are:

1) Wafer Mount

2) Wafer Saw

3) Die Attach

4) Snap cure/ Oven Cure

5) Plasma cleaning

6) Wire Bonding

7) Plasma cleaning

8) Mold

9) Post Mold Cure(PMC)

10) Trim&Form

11) Laser Marking

12) Testing

13) Finishing

There are mainly 2 types of line, which are ‘Autoline’ and ‘ Standalone line’. Each process is carried out by a specific type of machine. For ‘Wafer mount’, Mylar (Plastic Sheets) is sticked onto a wafer before sawing it. This is to prevent dust to fall onto the wafer’s die when sawing and the other purpose is for easy handling.The wafer is place on a wafer plate for handling.

Next is ‘Wafer saw’. This process is to cut the wafer into small pieces known as ‘Die’, small piece of circuit board. The wafer is saw for 2 times in order to prevent internal crack. When sawing, the wafer is rinsed with distill water for clensing purposes.

Next is ‘Die attach’, in this process, a Die is to be attached onto ‘Leadframe’ ( in matrix form 4 rows x 8 columns, 32 units in a leadframe). Before attaching a Die onto the leadframe, a polymer glue is paste on the leadframe. After that, by using programmed machine, each Die on the wafer is pick and paste onto the glued leadframe. On the wafer, there are ‘Ink Die’ which is Die that are rejected. The machine will read the Ink on the die and skip it for the next die.

Then, by using a transproter tray, each leadframe is sent to the ‘snap cure’ process to make the glue solid. The process takes approximately 2 minutes.

Next, is ‘Plasma cleaning’, this process is for cleansing purpose, but this process is optional, depending on the device requirement.

The next process is’Wire bonding’. In this process, connections are made between Die and leadframe by using 0.8mil gold wire. A capillary head is used to solder the wire in high temperature, it will form a ‘free air ball’ on the capillary tip and will be pressed onto the Die. This is known as 1^st bond. While for 2^nd bond, the capillary head will move to the leadframe and weld the wire onto it. There are altogether 48 bondings. Wire bonding is a very high speed and high precision process. But, the each leadframe will be checked for its quality in ‘Buyoff’ procedure. Buyoff consists of ‘Hisomet’ test, ‘Pull test’, and also ‘Ball shear’ test. Hisomet is to measure the length, width, height and loop of the ball bonding. Pull test is to test the strength of the wire bonding while Ball shear test is to test the strength of the ball’s bonding.

After that, the leadframe will go through another ‘plasma cleaning’ process (optional).

Next is the ‘Mold ‘ process. In mold process, ‘Resin’, a type of polymer will be melt with high temperature in the machine and then it will be encapsulate onto the leadframe and kept for pressure for several minutes.

Then, the leadframe will go through a ‘Post Mold Cure’(PMC) process. The purpose of this process is to make the polymer solid. This process takes around 2 hours.

Next is the ‘Trim&Form’ process. In this process, the leaframe is to be cut into small units. There are 1^st crop and 2^nd crop process. 1^st crop is degate removal and tie bar cut. 2^nd crop is end lead cut, final form, lead length cut and also singulation. After going through this process, each device will be a small sized chip.

After that, the units will be send for ‘Laser marking’ which is to marked the device number on it.

And then, the device will then send for’Hot and cold’ test. This is to make sure that the device can withstand high and low temperature and will be used in different places.

Finally is the’Finishing’ phase,which is packaging.

Day 3

Today, I was told to focus on the DA( die attach) and WB ( wire bonding) process. I was given some power point slides on the DA & WB. So, I was required to study and get a rough idea on how does these 2 processes do. I was granted permission to go to the line to see and ask operator for futher informations.

Day 4

Today, I was given some power point slides on OPL (One Point Lesson) and VI (Visual Inspection) procedures in DA & WB process. The OPL include tools using methods, methods of handling machine’s problems, glue and capillary changing procedures, leadframe handling methods and many more. I was to asked the operator how to handle all these problems.

Day 5

Today, I was exposed on how to do the ‘Buyoff’ procedures. There are ‘Hisomet test’, ‘ Pull test’, and also ‘Ball shear’ test. Hisomet test is to measure the length, width, height and also its loop using microscope and computer analyzer. Pull test is to test strength of the wire’s bonding. Ball shear test is to test the strength of the ball’s bonding. These 2 test are known as destructive test, which means that the unit will be damaged after the test and will be disposed.