Browse Prior Art Database

VIBRATION SOLDER PROCESS FOR OMPAC IC

IP.com Disclosure Number: IPCOM000008114D
Original Publication Date: 1997-Jun-01
Included in the Prior Art Database: 2002-May-20
Document File: 2 page(s) / 105K

Publishing Venue

Motorola

Related People

Stefan Lichterfeld: AUTHOR

Abstract

The problem that is discussed here is based on the soldering process of OMPAC Integrated Circuits (I&). The improvements provided by this paper include a more physical and chemical solder connection between the XC, its pads and the Printed Circuit Board (PCB) pads, an improved ageing per- formance and more reliable solder contacts under mechanical stress.

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MO-LA Technical Developments

VIBRATION SOLDER PROCESS FOR OMPAC IC

by Stefan Lichterfeld

INTRODUCTION

  The problem that is discussed here is based on the soldering process of OMPAC Integrated Circuits (I&). The improvements provided by this paper include a more physical and chemical solder connection between the XC, its pads and the Printed Circuit Board (PCB) pads, an improved ageing per- formance and more reliable solder contacts under mechanical stress.

PROBLEM(B) TO BE SOLVED

  On the bottom side of the IC a grid array of sol- der balls are placed and contacted to the IC junc- tion. A similar pad array is placed at a suitable and specified location. After adding fluxer paste to the PCB pads the IC is placed in its correct soldering location. The PCB is then heated in a solder oven where the solder balls melt and connect the IC to the PCB. Unfortunately it is not possible to verify the solder quality of the contacts as they are not now visible. There is of course a requirement for contact reliability. After ageing, through tempera- ture or mechanical stress, some IC contacts have been found to be suspect in this regard. Investigation on this effect showed a loss of solder contact on the IC pins which were not accessible after IC positioning.

  The problem is typically resolved by m-heating the PCB and carefully moving the IC, or removing the heated IC, adding new fluxer paste and resolder- ing the IC. The reason for this ageing effect is a physical solder ball contact, that does not provide any chemical contact when an initial current flow is applied, where the physical, non-chemical, solder ball contact tat easily brakes up under mechanical stress. A tiny amount of oxide or dirt is often a cause for solder not to flow on its pad. The fluxer itself is not able to guarantee that the heated solder ball surface brakes up all solder balls to provide the

molten solder. Hence, there is a need to improve the solder process to avoid any non-chemical solder contacts.

PROPOSED SOLUTION TO THE PROBLEM(S)

  To help the fluxer break up the solder surface or remove dust on the PCB pad, it is proposed to move the IC towards the PCB in a definable way whilst heating and re-flow soldering in the oven. It is pro- posed that the IC is moved by a mechan...