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Non-Component Edge Terminal and Pad Design

IP.com Disclosure Number: IPCOM000010730D
Publication Date: 2003-Jan-15
Document File: 4 page(s) / 52K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that eliminates component terminals at the longer or shorter edge of the component. Benefits include reducing the wetting force F4, which plays a major role in lifting the component from one terminal (i.e. tombstoning).

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Non-Component Edge Terminal and Pad Design

Disclosed is a method that eliminates component terminals at the longer or shorter edge of the component. Benefits include reducing the wetting force F4, which plays a major role in lifting the component from one terminal (i.e. tombstoning).

Background

Tombstoning is a common failure mode in surface mount technology. The problem becomes more serious as components become smaller (i.e. 0402 and 0201). Figure 1 shows how tombstoning happens in two ways:

1.      There is a difference in the time of melting between two pads.

2.      There is a difference in the wetting forces between two pads.

Currently, tombstoning is solved by reducing the stencil aperture opening on the solder masked pad that reduces the amount of paste deposited on the pads (e.g. change the 1:1 stencil aperture to an oval shape as in Figure 2). This reduces the difference in pulling force between the two terminals. However, this solution uses insufficient solder which can sacrifice solder joint reliability, especially when the stencil is clogged.

General Description

The disclosed method eliminates component terminals at the longer or shorter edge of the component. The terminals are designed at the middle of the component (see Figure 3). This design reduces the wetting force F4 which plays a major role in tombstoning.

The terminal width that the wetting force F4 formed is very small compared to the current state of the art. Also, the major wetting force formed in this design is...