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MECHANICAL ALIGNMENT OF C5 ICs WITH THREE CORNER PEG CONCEPT USING LARGER SOLDER SPHERES

IP.com Disclosure Number: IPCOM000006259D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2001-Dec-19
Document File: 2 page(s) / 96K

Publishing Venue

Motorola

Related People

Kiron R Gore: AUTHOR [+3]

Abstract

1. C-5 ICs typically require robots with sophisticated look up vision capability for assembly onto circuit boards. Robots are necessary as silhouette imaging used by chip shooters are not accurate in that the edge to ball pattern tolerance is unreliable and adversely effects placement quality, 2. C5 assembly is considered a "blind" assembly as a visual aid cross check is not available to verify place- ment accuracy. This makes it diflicult not only for robots (by putting stringent placement accuracy requirements) but also for humans for a manual repair process.

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MOTOROLA INC. Technical Developments Volume 14 December 1991

MECHANICAL ALIGNMENT OF C5 ICs WITH THREE CORNER PEG CONCEPT USING LARGER SOLDER SPHERES

by Kiron R Gore, Ved V. Gundotra and Edward J. Hall

PROBLEM DEFINITION

1. C-5 ICs typically require robots with sophisticated look up vision capability for assembly onto circuit boards. Robots are necessary as silhouette imaging used by chip shooters are not accurate in that the edge to ball pattern tolerance is unreliable and adversely effects placement quality,

2. C5 assembly is considered a "blind" assembly as a visual aid cross check is not available to verify place- ment accuracy. This makes it diflicult not only for robots (by putting stringent placement accuracy requirements) but also for humans for a manual repair process.

3. Fluxing of the under side of the IC is required for two reasons; first to act as a catalyst during reflow and second to provide a tacking media during transporta- tion. Over fluxing causes the IC to float away when the flux liquifies. Under fluxing does not provide enough tackiness during transportation.

4. Average cycle time for a robotic assembly process involving look up vision and fluxing is 12 to 15 sec- onds; which is high.

5. Orientation errors could occur during assembly since there is no physical feature defining the same.

DESCRIPTION OF

THE NEW CONCEPT

  The solution for C5 chip carrier alignment is to uti- lie larger 0.050" dia. solder spheres on three 0.030" dia corners pads. After reflow these spheres will sit 0.015" higher than the rest of the 0.030" dia spheres that were reflowed on 0.030" dia pads. When assembled on the PCB these comer balls now act as posts that self center and sit into a plated blind via or thru hole of 0.040" dia. Due to the self...