Browse Prior Art Database

DEAD-BUG TO LIVE-BUG COPLANARITY ALGORITHM

IP.com Disclosure Number: IPCOM000006391D
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2001-Dec-31
Document File: 2 page(s) / 132K

Publishing Venue

Motorola

Related People

Roger Paul Stout: AUTHOR

Abstract

"Coplanarity" is an important IC-packaging speci- fication. It is typically applicable to SMT (surface mount technology) IC packaging technology, and is defined as the deviation of each lead of the part from the "seating plane" of the part (see Figure 1). "Dead-bug" coplanarity is the term used to describe the coplanarity which results when the leads of the part are not carrying the weight of the part during measurement (such as might arise if the part is upside-down with its leads pointing upwards, or if the part is right-side up but resting on a pedestal with the leads completely suspended in the air). "Live-bug" refers to the coplanarity of the leads when they are car- rying the weight of the part (as in Figure 1). With ever increasing package weight, the dilference between dead- bug and live-bug coplanarity is not negligible, and can therefore influence product yield.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 46% of the total text.

Page 1 of 2

MOTOROLA INC. Technical Developments Volume 15 May 1992

DEAD-BUG TO LIVE-BUG COPLANARITY AL@ORITHM

by Roger Paul Stout

  "Coplanarity" is an important IC-packaging speci- fication. It is typically applicable to SMT (surface mount technology) IC packaging technology, and is defined as the deviation of each lead of the part from the "seating plane" of the part (see Figure 1). "Dead-bug" coplanarity is the term used to describe the coplanarity which results when the leads of the part are not carrying the weight of the part during measurement (such as might arise if the part is upside-down with its leads pointing upwards, or if the part is right-side up but resting on a pedestal with the leads completely suspended in the air). "Live-bug" refers to the coplanarity of the leads when they are car- rying the weight of the part (as in Figure 1). With ever increasing package weight, the dilference between dead- bug and live-bug coplanarity is not negligible, and can therefore influence product yield.

  If the leads are carrying the weight of the part dur- ing actual package-to-board assembly, then live-bug coplanarity data will have more bearing on the actual success of assembly than will dead-bug data, and would therefore be preferred by most customers. However, there is some risk imposed on the parts during live-bug coplanarity measurements. Further, it should be noted that live-bug inspections are not even possible for parts which have had their leads formed, but have not yet been separated from their molded carrier ring (MCR), yet this is the shipping format which may begin to be required by customers precisely because of the safety it affords to the leads.

  These problems can be addressed by an algorithm which allows one to take dead-bug coplanarity data and convert it to its corresponding live-bug values. Although it has been developed and implemented on a PC, it could be embedded directly into the software of typical lead- inspection equipment. Use of this algorithm would per- mit one to take only dead-bug measurements, yet present it to the customer either dead-bug or live-bug data, or both, as preferred.

The direct goal of the algorithm is to determine how the weight of the part is distributed among the various

28

leads, given that each leadi'has some initial height above some reference plane (the'lraw dead-bug data). By defi- nition, in the live-bug condition all load-carrying leads have zero coplanarity, but their deflected positions detine the seating plane, and from this plane are calculated the live-bug coplanarities ofall the remaining leads.

  A multi-leaded part c!m be considered as a spring- mass system, where each individual lead is idealized as an identical spring (whose spring-rate can be cal- culated based on nominal lead geometry and material properties). Each lead which touches the "seating plane:' and only those leads, will therefore store an amount of mechanical energy which depends on its spring-rate and its deflection....