Product Features for Daily Thermal Profiling

EASY - QUICK - PRODUCTION FRIENDLY - SURVIVABLE

PCB Assemblers' Demands Drive Reflow Oven Profiling Technology: Today's assemblers seek thermal profiling equipment that provides cost-effective technology for daily use in production. by Martin Ingall, Phil Manto and Nissim Sasson

A shorter version of this article was published in the Electronic Packging & Production (EP&P) magazine.

The concept of performing thermal profiles for reflow soldering is now widely accepted throughout the printed circuit board assembly industry. Thermal profiles are performed on a board-by-board basis during prototyping or at the time of assembly start-up. The desired thermal profile then should be safeguarded and its parameters maintained when running boards.

The past 10 years have seen the homogenization of commerically available thermal profiling technology. This has been simultaneous to improved understanding among production and process engineers of their basic profiling needs. Where are we now? There are two answers.

First, managers and engineers at surface mount facilities already owning thermal profilers are frustrated by their underutilization. Traditional thermal profiling is time consuming and inconvenient. Additionally, the complexity of data packages and reliance on software analysis disqualifies these devices from real-time production application. Managers are dissatisfied because they want continuous process control and reporting. The paradox: process engineers know that daily profiling is necessary and that production departments would like to perform this task. Yet, both know that manufacturing engineers and technicians often do not have the time or expertise to endure the tediousness of a standard thermal profile. So process engineers continue to do the best they can, by at least establishing an initial profile.

Second, many plants which have not yet acquired a thermal profiler continue to put off such a purchase due to good education and prudent spending. Managers now know that practical, production-oriented thermal profiling is what they need. They also recognize that spending money for a thermal profiler that is not accessible or used regularly by machine operators is of limited value.

Today's PCB assembler demands for thermal profiling equipment can be summarized in one phrase: cost-effective technology for daily use in production. There are five basic demands in this area: ease of use, immediate access to data, simplification of software, survivability and price.

Ease of Use

Once a direct thermal profile has been performed on a board, the dilemma of monitoring oven performance and the board profile itself becomes apparent. To solve this problem, manufacturing managers now seek reference profiles for their board and independent oven monitoring after initial, direct profiling. That calls for prefabricated thermal sensor cards with high quality, permanently affixed top-side and bottom-side thermocouples that can be used repeatedly and indefinitely. (Fig.1) This relieves the need to affix thermocouples directly to a board each time a profile is desired, thereby saving time and product.

Another trouble spot is the need to frequently recharge the power pack of conventional thermal profilers. Design improvements and economics in energy consumption now permit simple battery packs to power profilers for more than 1000 runs, without hassling with recharging stations or power packs - yet another step towards ease of use.

Ease of use also means the ability to run a thermal profiler repeatedly without the immediate need to download data to a PC. The profiler's memory should be able to store multiple runs, permitting the user to collect an entire bank of data for analysis. That means less time on the computer and more time directly attending to the production line.

Fig. 2 Reflow module inputs thermal profile data to its own display at oven. Press to enlarge

Immediate access to data

Manufacturing engineers and technicians now demand immediate access to entire sets of run information when their profiler exits their oven. The development and availability of at-oven LCD displays permit the instant viewing of the important temperature and peak area information. (Fig. 2)

Equally important is the automated extraction of data from the temperature graph in simple, practical form. When this is accessible to the oven technician on his or her demand, it means instant response to oven performance deviations and operator errors. This response happens before boards are run each day, effectively transferring the identification of defects form post-facto board inspection to pre-run process control. This is critical for today's demands for high quality, fast turnaround with process documentation run by run.

This is a dramatic and most welcome development. It transfers the use of thermal profilers from setup and troubleshooting to daily, preemptive process control. In this sense, the much older field of thermal profiling is just catching up to the newer process control procedures of wave soldering, which were brought about by board-wave interaction measurement capabilities introduced to wave soldering only several years ago.

Fig. 1 Simplified software shows thermal profiles from the utilization of a thermal sensor card whereby three thermocouples are employed successfully. Press to enlarge

Simplification of Software

Manufacturing managers know that software must by simple to navigate and read in order to tabulate and graph core information. They know that quality happens in production every day, every shift, and that real-time reporting based on daily information is the key to complete defect reduction and process control. Likewise, while engineering, process control, prototype and QA departments may have the mission of extensive thermal profiling and detailed analysis, they know that without regular (daily) monitoring of the process, their prescriptions have limited value.

There is also a demand for software designed for use by machine operators and engineers alike on a daily basis. While managers and engineers no longer want to be the sole, exclusive proprietors of all software use, competition has driven profiler vendors to develop an ever-expanding labyrinth of software features. Now, look for newer software to offer simplicity and still meet all of the feature requirements for most users. The key here is utility, not sophistication.

Survivability

Thermal profilers operate in harsh environments. Consequently, their life span often ends after about two years of regular use. If this is true, the thermal profiler has become a consumable and defies the definition of even a small capital equipment purchase.

Fig. 3 Superior thermal barriers for reflow profilers reduce internal temperature for achieving indefinite survivability. Press to enlarge

Unlike conventional asbestos sleeves, steel boxes and internal heat sinks, advances in materials science now permit superior thermal barriers for profilers. (Fig. 3) These yield internal profiler temperatures some 30?C lower than what was previously attainable. Such materials are the direct result of civilian application of military technologies. Indefinite survivability of thermal profilers is now possible, vastly enhancing the cost-effectiveness of their purchase.

Price

Last, but not least, is price. Assembly plants are confounded that years of intense competition among profiler vendors has not resulted in demonstrable downward price pressure. Instead, profiler costs have crept up year to year, particularly with the addition of numerous bells and whistles. Low-cost thermal profilers - in the $2000 range - which respond to the new user requirements, are now stepping into this void. Their affect on the marketplace and, more importantly, on process control procedures for surface mount assembly, has finally taken hold.