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Method and Fixture for Surface Mount Solder Reflow of Printed Circuit Board Assembly Containing Temperature Sensitive Components

IP.com Disclosure Number: IPCOM000237213D
Publication Date: 2014-Jun-09
Document File: 2 page(s) / 46K

Publishing Venue

The IP.com Prior Art Database

Abstract

A method and fixture for surface mount solder reflow of printed circuit board assembly (PCBA) containing temperature sensitive components is disclosed.

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Method and Fixture for Surface Mount Solder Reflow of Printed Circuit Board Assembly Containing Temperature Sensitive Components

Disclosed is a method and fixture for surface mount solder reflow of printed circuit board assembly (PCBA) containing temperature sensitive components.

Surface mount components (SMC) are typically attached to a printed circuit board assembly (PCBA) by a solder reflow process inside a conveyorized oven. The SMC are typically rated for a specific maximum peak temperature and time above liquidus (TAL) which is the melting point of the solder alloy. There are joint industry standards (J-STD) that typically specify limits of 260C max. temperature and a 150 second TAL for SMC. If a component does not meet this J-STD specification, the component is classified as a temperature sensitive component (TSC).

The problem solved by this disclosed method and fixture is the violation of the J-STD max. temperature and the Time Above Liquidus (TAL) limits in PCBA reflow processes. The high frequency of occurrences for this problem is typically on large size PCBAs that have a wide range of component thermal mass. Smaller size components heat up faster than larger size components during the heating ramp. Known solution to this problem is to shield and add thermal compensation to smaller size components to equalize the mass across the PCBA during reflow. The drawback of such a solution is that by shielding the lower mass components from the heating phase, it also shields them from cooling efficiently. Another method and fixture solution is needed to provide a higher cooling efficiency that is needed to reduce the TAL of both TSCs and non-TSCs. The component industry has been reluctant to support temperature and TAL beyond what they had already specified in their product data sheet.

The disclosed method and fixture shields the lower mass components on the PCBA during the heating phase of the reflow process and also enables the removal of the shield from the PCBA...