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Method for an antitombstoning capacitor

IP.com Disclosure Number: IPCOM000020309D
Publication Date: 2003-Nov-12
Document File: 3 page(s) / 90K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for an antitombstoning capacitor. Benefits include improved yield.

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Method for an antitombstoning capacitor

Disclosed is a method for an antitombstoning capacitor. Benefits include improved yield.

Background

         Tombstoning is a failure mode that occurs during the soldering process that attaches a capacitor to a circuit board. One cause of tombstoning is uneven solder flow. When the solder on only one side of the capacitor wicks, tension is created on the side with the molten solder. The opposite side is lifted, creating an open circuit. This problem is conventionally solved in many ways, including:

•         Adjusting the circuit board land pattern

•         Modifying the reflow oven profile

•         Reducing the amount of solder paste

•         Improving the accuracy of the cap placement location on the circuit board prior to reflow

•         Using a paste that releases less gas during reflow

         At a given temperature and surface condition, solder flows at a constant rate. When the distance the solder travels is increased, the time is also increased. Fluids travel slower when the normal fluid motion is interrupted, such as when traveling over a rough surface rather than a smooth surface.

         The conventional state-of-the-art (SOTA) method is comprised of three stages (see Figure 1):

1.         Prior to eutectic temperature

2.         During eutectic temperature when uneven solder flow can occur and uneven forces are applied

3. Post-eutectic temperature when only one side reflows

During stage 2, the solder is fluid. The flow is not interrupted and travels at maximum speed.

General description

         The disclosed method is a capacitor that resists tombstoning by inhibiting uneven solder wicking. One or more grooves on the capacitor terminal sides increase the surface area that the solder must flow across during the circuit board attach process. The grooves provide a rough surface that disrupts the fluid motion, increasi...