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To Receive these FREE SMT Technical Papers please call 631-981-7081 or send E-mail to sales@research-intl.com
Past Issues Of Research International Sponsored SMT Magazine "Tech Notes"
Issue #12 - TOWER Reflow Oven Self-Profiling
Issue #11 - February 1999 "How No-Clean Reflow Solders More Boards"
Issue #10 - February 1998 "Modular Vertical Stationary Reflow for High Volume SMT Assembly - Commonly Asked Questions"
Issue #9 - February 1997 "Temperature Control of the Reflow Process"
Issue #8 - February 1996 "How to Profile a PCB"
Issue #7 - February 1995 "Stop Solderability Problems Before You Get to the Boards"
Issue #6 - February 1994 "The Performance Triangle for Inert Atmosphere Ovens"
FUNDAMENTALS OF BGA BALL ATTACH REFLOW PROCESS
by
Research International
Abstract
The fundamentals of reflowing solder balls for the BGA ball attach process is discussed. The content is divided into three major sections: modes of heat transfer, convection technologies used in reflow ovens and mechanics of temperature profiles.
MINIMIZING NITROGEN CONSUMPTION IN A CONVECTION REFLOW OVEN
by
J. Pierre Menard
Design Engineer
Research International
Abstract
Changes in SMT assemblies such as large mass differences between components, ball grid arrays, and varied product mix have driven most manufacturers to convection reflow ovens. Changes in the reflow process such as advances in no-clean paste, fine pitches, and bare copper assembly have driven the market to nitrogen reflow ovens. Convection reflow ovens, requiring large amounts of fluid flow, directly oppose the conditions favorable for an economic, stable nitrogen reflow oven.
Four basic approaches to minimizing nitrogen consumption are possible. The nitrogen is recirculated one or more times to facilitate heat transfer without increasing nitrogen consumption. The principles of heat transfer are applied to maximize the heat transferred per unit of nitrogen. Each printed circuit board is profiled, minimizing nitrogen flow and convection heat transfer taking advantage of process window limits. Physical barriers are added to protect the cavity from oxygen contamination. Each approach is examined, and the engineering trade-offs of each are discussed. Nitrogen consumption can be reduced with a balance of all the options.
STATISTICAL PROCESS CONTROL OF A REFLOW OVEN
by
Research International
Abstract
The need for Statistical Process Control (SPC) is already established:
Remaining competitive and profitable requires extremely low rejection rates. Advance complicated boards and packaging requires tight control and tracking of all the process variables. ISO Certification requires documented control of the process variables.
A short review of statistical process control principles will be discussed. Examples of how SPC can be applied to the reflow process will be shown.
OPTIMIZING PRINTED CIRCUIT BOARD COOLING
by
Research International
Abstract
Printed circuit board cooling was optimized without compromising the integrity and robustness of the inert atmosphere convection oven. The PCB assembly market required the following features incorporated into a purge/cooling zone:
User control over cooling rates from 1 to 5 degrees C.
Oxygen levels in the reflow section of the cavity less than 35 ppm and less than 100 ppm until the board is cooled below 150C under full production load conditions.
Minimal nitrogen consumption at less than 500 CFH.
An easily cleaned surface where solder flux condenses.
Continuous supply of cooling water is not required (closed loop system).
The changes in the PCB assembly process that have focused attention on cooling are briefly discussed. A design for a purge/cooling zone is submitted that meets the specifications. The theoretical results are modeled by a spreadsheet, and empirical results show excellent correlation to the spreadsheet, verifying the design and use of a spreadsheet as a profile predictor.
OPTIMIZING NITROGEN PURITY AND FLOW IN A CONVECTION REFLOW OVEN
by
Norman R. Cox
Engineering Manager
Research Inc., Assembly Automation Division
Abstract
SMT assemblies consist of larger components with tighter spacing between the components. Trends towards fine pitch and no-clean soldering also affect the reflow oven. Specifically, new ovens need a higher convective heating content and be capable of reflowing in an inert atmosphere. This paper will address convection heat transfer, nitrogen atmospheres, and specifically address an oven that is designed to accommodate both processes simultaneously.
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