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Method for IC open-joint testing at PCB assembly through emission spot analysis

IP.com Disclosure Number: IPCOM000012705D
Publication Date: 2003-May-21
Document File: 2 page(s) / 57K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for integrated circuit (IC) open-joint testing at printed circuit board (PCB) assembly (PCBA) through emission spot analysis. Benefits include an improved test environment and improved reliability.

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Method for IC open-joint testing at PCB assembly through emission spot analysis

Disclosed is a method for integrated circuit (IC) open-joint testing at printed circuit board (PCB) assembly (PCBA) through emission spot analysis. Benefits include an improved test environment and improved reliability. 

Background

              PCBA testing becomes increasingly challenging as the industry continues its trend toward smaller and denser products. PCB space limitation and high-speed PCB design challenges designers to allocate sufficient test points for conventional in-circuit test (ICT) to catch open-joint failure. A node is not tested at ICT if no test node is present.

              Boundary-scan devices are used in circuit design wherever possible to form a chain for PCBA testing to reduce the test point requirement. X-Ray inspection is performed at the front of the assembly line to inspect short/open joints but cannot detect ball grid array (BGA) open joints effectively. Functional test further screens out open joint defects but is poor at detecting pin isolation.

General description

              The disclosed method detects IC open joints at PCBA through emission spot inspection. An emission microscope is used to inspect emission spots that are induced by electron holes at the silicon. A captured emission spot pattern at the silicon level indicates open joints.

              Functional test vectors are sent across existing silicon circuits to exercise each device pin to generate an emission spot. A lifted pin causes the silicon circuit to not toggle or idle and forms a different emission pattern. The captured emission pattern is compared against a learned pattern to detect open joints.

              Alternatively, a controlled cell enable/disable signal is sent to the p-n junction embedded at silicon on each device pins. Each pin is exercised with test vectors across the cell to generate an emission spot. The cells can be arranged in predefi...