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Noble metal PPF soft solder anti bleed leadframe design

IP.com Disclosure Number: IPCOM000173746D
Original Publication Date: 2008-Sep-11
Included in the Prior Art Database: 2008-Sep-11
Document File: 2 page(s) / 218K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

A common problem in pre-plated frames (PPFs) is the undesired wetting of solder, the so called solder bleeding. Especially the high dissolution of solder into the Au/Ag layer in PPFs causes severe solder bleeding during the die and chip attachment. The solder bleed out is accompanied by several disadvantages: a larger solder surface (Figure 1), the covering of the mold lock feature (Figure 2), thinner bond line thickness (Figure 2), solder bleed reaching the die pad bottom (Figure 2), solder bridging in chip by chip packages (Figure 3) and tilting of chips (Figure 4). To date, glue is commonly used in PPF packages in order to prevent solder bleeding. However, glue is not suitable for high power packages in which soft solder is used as die attach material.

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Noble metal PPF soft solder anti bleed leadframe design

Idea: Bharathi Ranjit Singh, MY-Malacca; Yong Chern Poh, MY-Malacca; Fong Lim, MY-Malacca;

Jagen Krishnan, MY-Malacca

A common problem in pre-plated frames (PPFs) is the undesired wetting of solder, the so called solder

bleeding. Especially the high dissolution of solder into the Au/Ag layer in PPFs causes severe solder

bleeding during the die and chip attachment. The solder bleed out is accompanied by several

disadvantages: a larger solder surface (Figure 1), the covering of the mold lock feature (Figure 2),

thinner bond line thickness (Figure 2), solder bleed reaching the die pad bottom (Figure 2), solder

bridging in chip by chip packages (Figure 3) and tilting of chips (Figure 4).

To date, glue is commonly used in PPF packages in order to prevent solder bleeding. However, glue

is not suitable for high power packages in which soft solder is used as die attach material.

As solution of the presented problem, it is now proposed to use a novel solder resist that consists of a

polymer based material with non wetting properties. The solder resist adheres to the surface of the

leadframe (Figure 5) and acts as a barrier around the circumference of the chip placement area before

the die attachment process. For this purpose, it is also designed with a thickness larger than the

solder bleed...