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November 17, 2008

Lead Frame Contamination

What is the best way to check to make sure an incoming lead frame is free of any contamination before the Die Bond process? Is there a preferred cleaning process or inspection method?

S. H.

Expert Panel Responses

The answer is really a 2 part solution to this request. First, Lead frames need to be free from all surface organics organic compounds and or residues - this can be reviewed with a scanning electron microscope and or high powered scope. The object is to validate there is no residues present on the surface. Some companies use a SEM / EDX to quantify the carbon and oxygen present and if it is high then a Fourier Transform Infrared Spectrometer (FTIR)is used to determine the organic spectrum present to determine the type of organic present. This is a good analytical tool to use to verify surface contamination. The second part is also using a SEM / EDX to determine the quality of the gold that is plated and this is used to determine the organic levels plated into the gold . All gold baths have organic chemistries and brighteners in its gold solution. This test is used to verify the bath is kept in balance and there are not elevated levels of organics plated in to the gold plating. The next answer addresses the need to plasma etch the lead frames before wirebonding to insure that all organics are gone and that the gold plated surface is prepped for wirebonding. Plasma etching is a great process step (CLEANING) before wirebonding to insure the lead frames are cleaned properly before wirebonding. Plasma removes the organics and oxides present on the surface and preps the gold surface. We can also provide plasma etch advise if this is of interest.

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Mark McMeen
VP Engineering Services
STI Electronics Inc.
Mark T. McMeen is STI Electronics Inc.ʼs Vice President of Engineering Services. He oversees the daily operations of the Engineering Services division of STI. He has over 18 years experience in the manufacturing and engineering of PCBs.

I'm not sure what methods you or others use now to determine incoming cleanliness other than visual and yield loss. Since adhesion between the lead-free and the die is critical, the surfaces must not only be particulate free, but free from any ionics, anti-oxidants or rust inhibitors, oils, etc. Good news is there are several cleaning processes available today that can deliver clean lead frames reliably.

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Craig Hood
Director of Intl Sales and Global Marketing
Petroferm Inc.
Mr. Hood is Director of International Sales and Global Marketing for Petroferm's Cleaning Products Division, a manufacturer and supplier of cleaning agents for defluxing and stencil cleaning.
NOTE: Mr. Hood is no longer working at Petroferm Inc.