The Ultimate Guide to Lead Frame

Lead Frame Overview


A lead frame is a generic term for a type of (mostly) low-cost IC package assembly used for DIL types packages as well as PLCCs and QFNs.


The frame is typically made of a thin layer of copper, though other materials, such as aluminum and even gold, have been used. The die is glued to the frame; conductive adhesives are common, as a die substrate is typically ground, though non-conductive die attach is also possible; the adhesive can be dispensed by syringe – the most common method – or an adhesive tape can be applied; the die is placed onto the frame and the die pad wire bonded to the leads; as can be seen in the image copied below, the leads are not in direct contact with the die pad; not shown is the outer metal of the frame that holds the leads in place; this is cut, sawn or etched away when the package body has been formed (molded) to keep the leads in place.


The leads then carry the signals and power to and from die to the outside of the package. If the lead frame is copper the exposed leads of the package are plated with nickel or tin (or gold) to avoid oxidation.


The package body itself is typically a plastic or resin compound, though ceramic bodies are also possible especially if the assembly will generate or be subjected to high-temperatures.



Manufacturing of Lead Frame


The frames are formed on a flat plate of metal, with multiple frames connected together. Segregation, as mentioned earlier, is achieved by punching, sawing or etching. Etching is used for high density leads as is can give much closer tolerances and finer detail; high-density QFN (close to die size) type assemblies are typically etched. For low lead density and larger package assemblies the preferred process is stamping, which is usually employed in high volume production runs. The process of stamping is automated and runs at a very high speed, allowing you to deal with high loads and volumes and distribute the initial tooling costs which may be too much for low volume productions.



Overtime, as our standards evolve and our demands grow bigger, there has been a requirement for much more precision in the manufacturing and packaging process of integrated circuits and semiconductors. Customers want high functioning lead frames to use in highly complex and complicated devices, which is why the use of precision engineered lead frames is becoming more and more commonplace.


The Importance of a Good Lead Frame


It is extremely essential for the performance and efficiency of ASIC that the lead frame used is of high quality and does not have any structural or functional defects. A defective or damaged lead fame can lead to disastrous consequences for your ASIC as the performance and reliability of the chip will be severely compromised.


There are many kinds of lead frames, each characteristic varying based on what is required by the user. Lead frames can vary in terms of their electrical and thermal properties and have a plethora of specifications and features that can be customized based on the design that the user wants to implement.


(special thanks to Goofy!)

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