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A Test for Flux Entrapment

IP.com Disclosure Number: IPCOM000061942D
Original Publication Date: 1986-Aug-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Goho, J: AUTHOR

Abstract

A non-destructive qualitative test is provided in flex circuit soldering for determining whether flux is trapped between the flex circuit dielectric and a stiffener to which it is attached. Flex circuits are frequently adhesively attached to stiffeners to provide mechanical rigidity for that portion of the circuit which does not need to be flexible. The flex circuit is first wave soldered and cleaned. If solder flux remains on the flex circuit after these operations, it is subsequently trapped in the adhesive operation. If that happens, over time the flux corrode the vias, and may even penetrate to the electronics on the opposite side of the flex circuit. This test detects whether flux has been trapped in this manner.

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A Test for Flux Entrapment

A non-destructive qualitative test is provided in flex circuit soldering for determining whether flux is trapped between the flex circuit dielectric and a stiffener to which it is attached. Flex circuits are frequently adhesively attached to stiffeners to provide mechanical rigidity for that portion of the circuit which does not need to be flexible. The flex circuit is first wave soldered and cleaned. If solder flux remains on the flex circuit after these operations, it is subsequently trapped in the adhesive operation. If that happens, over time the flux corrode the vias, and may even penetrate to the electronics on the opposite side of the flex circuit. This test detects whether flux has been trapped in this manner.

In the test, an indicator, cobalt dichloride, a polar molecule which will mix readily with similar polar groups, is mixed with a water reduceable flux to form a homogenous solution. The solution is applied per normal flux operation. The ratio between the flux and cobalt dichloride varies depending upon the sensitivity required. The flex circuit is then sent through wave solder and cleaned in the normal manner. The part is then dried and placed in an X-ray Fluorescent Spectrometer (XRF) with the dielectric of the flex circuit facing the X-ray beam. The cobalt peak occurs at 6.92 KeV. If cobalt is seen, then flux entrapment has occurred.

This test provides a simple, non-destructive non-ambiguous method by which organics from...