Supply Forms for Bare
Die - The concept
Once the wafer has been sawn the next process the bare die must undergo
is determined completely by the die supply form the customer requires.
There are two main factors which drive choice of the end bare die supply
form
1. The capacity for the product to be handled safely and stored
appropriately without deterioration of physical & electrical quality.
2. The suitability for the customers manufacturing process at their end.
Packaging
Safe carriage of the bare die is important to maintain overall quality
and ensure the best yields when they are assembled. It is paramount to
pick the appropriate carrier conditions for the bare die. For example,
allowing a wafer freedom to move within its container is extremely
likely to cause major damage during transport. Although the previous
example may seem like common sense, the reality is that a combination of
factors such as allowable movement, topside surface contact,
susceptibility to ESD (Electro-Static-Discharge) or even exposure to air
can contribute to the correct choice of bare die carrier. Through long
term practical experience and a developed knowledge of the available
carriers Die Technology as your franchised die distributors are well
equipped to advise those new to using bare die on the best method for
them.
Storage
Another safety factor to consider in choosing the correct die supply
form is the method in which the bare die are stored. Improper storage no
matter how appropriately the bare die have been carried will still
result in defective product at the point of assembly. Due to both the
physical and electrical sensitivity of the material, life of a bare die
product is severely affected by the conditions in which the dice are
stored. There are two major problems the bare die user is faced with,
the first is electrical protection, all die product must be protected
from ESD (Electro Static Discharge), circuit tracks can deteriorate due
to the excessive ESD charge forced through them therefore dropping the
overall performance of the dice. In the worst cases the dice can be
destroyed entirely!
The second problem is direct corrosion of the physical bare die surface
which occurs when the dice are not stored in the right atmospheric
conditions. If dice are stored in air then the result is a high level of
oxidisation growth on the bare die surface which renders the die
unusable, another important factor to consider is the level of
cleanliness in the storage area, the number of foreign particles in the
atmosphere surround the bare die can still result in 'dirty' die and a
drop in product quality. The essentials needed for a basic level of bare
die storage are to contain the die within an Electro Static Preventative
carrier stored within an atmosphere of nitrogen to preserve the
metalisation quality. Once again Die Technology as your die distributors
can provide technical advice on this issue or alternatively store your
die product for you where necessary.
End Use
The final contributor to choosing supply form is purely practical and is
determined by the type of operation due to be performed on the bare die
at the customer’s facility. Speed and accuracy often determine this, for
example a customer may request that bare die product remains sawn on its
ring frame in order to increase the speed it can be processed at their
end. This speed is usually associated with equipment such as an
automatic Pick & Place machine where the bare die can be rapidly removed
from the foil. For example, Ring frame supply form is ideal for those
looking for a fast turn-around or high volume as equipment can easily be
calibrated for fast processing due to the linear nature of the bare die
orientation. For customers using higher volume machines they may wish to
perform this task with minimal need for equipment calibration to size &
orientation and would in this instance request a 'Tape & reel' option
from the distributors where the bare die are placed directly into a
pre-defined tape with set dimensions and can literally be fed
automatically into a rapid assembly machine. (see tape & reel picture
below). However, flexibility in handling can also be an important
requirement and is usually related to medium to low volume dice
requirements, the most common supply form chosen here is bare die in
waffle pack. Supplying die in waffle pack allows assembly by both manual
and automatic methods and is considered to be the most versatile carrier
form overall in terms of handling, die orientation and storage lifespan.
In summary choosing the right supply form boils down to level of
experience in handling bare die, knowledge of the correct storage
conditions and the appliance of practicality in relation to the products
future assembly process and equipment that will be used. As franchised
die distributors we should be well equipped to advise those unsure in
this choice.
Supply
Forms - The Process
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National Semiconductor