Browse Prior Art Database

SMT Via in Pad Assembly ,Method and Use There of

IP.com Disclosure Number: IPCOM000015789D
Original Publication Date: 2002-May-27
Included in the Prior Art Database: 2003-Jun-21
Document File: 3 page(s) / 1M

Publishing Venue

IBM

Abstract

Solder joint reliability is jeopardized when thru and blind vias are used on functional surface mounting device pads. By filling these thru and blind vias with additional solder paste during the screening process, sufficient volumes of paste can be applied to reliably form the interconnection of electronic component to circuit board substrate. Thru and blind via volumes can be calculated before hand , during the stencil design stage of process development. Now sufficient paste volume may be added to individual SMT area of the PCB prior to reflow step.

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SMT Via in Pad Assembly ,Method and Use There of

   Solder joint reliability is jeopardized when thru and blind vias are used on functional surface mounting device pads. By filling these thru and blind vias with additional solder paste during the screening process, sufficient volumes of paste can be applied to reliably form the interconnection of electronic component to circuit board substrate. Thru and blind via volumes can be calculated before hand , during the stencil design stage of process development. Now sufficient paste volume may be added to individual SMT area of the PCB prior to reflow step.

*Nokia 3310 Card - N502 Leadless Chip Carrier

*Close-up photos are of a raw card referencing the thru holes in SMT pads located at different sites.

Stencils that are used for screening paste have openings, dimensions of which are based on the actual pad dimensions. It is not uncommon to have capacitor pads with through drilled vias, which provide internal power connections. Even a very small diameter via can 'rob' almost 50% of the available solder volume. This depletion of solder can result in non-wet or poorly wetted solder joints leading to excessive repair.

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A common industry practice is to move the board to a bench repair operation where an operator would manually add solder to all joints (illustrated above) with insufficient solder. This bench repair technique is a very subjective and time c...