Book Excerpt: The Printed Circuit Assembler’s Guide to... Factory Analytics, Chapter 3

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Excerpt from: The Printed Circuit Assembler’s Guide to... Factory Analytics, by Julie Cliche-Dubois, Cogiscan

Chapter 3: SMT Data Analytics: Oven to AOI
The latter half of the SMT process is all about soldering the SMT components to the PCB and verifying the accurate placement of those components to help ensure the functionality and reliability of the unit. In this chapter, we’ll look at the important analytics for the reflow oven and automated optical inspection (AOI) machine.

Oven
While not the “sexiest” machine on the line, the reflow oven is a critical element of the SMT process by facilitating the melting of solder paste to form both reliable and durable solder joints. Dialing in the oven process, especially in high-mix scenarios, is something of an art form: the various nuances and adjustments with temperatures and conveyor speed between jobs can be incredibly complicated. If not carefully managed, it can jeopardize the overall quality and reliability of PCBAs produced.

LINE OPERATOR: Maintenance schedule is of the utmost importance with a reflow oven—keeping that beast up and running is key. Any unexpected break with an oven is rarely simple, and the line operator doesn’t want the line to go down in order to fix a broken heater in the oven. And any units running in the oven during a malfunction and/or breakdown will probably get scrapped (burned).

The line operator needs to be warned at the start of the reflow operation if the actual/measured zone temperatures are too far from the set/programmed temperatures. Ideally, line interlocking should also be performed (if a complementary shop floor control system is in place). This not only applies during production but is also important immediately following a recipe change during changeover. Reflow ovens may need up to 45 minutes to stabilize on a new recipe if the new zone temperatures differ greatly from the current program.

MANUFACTURING ENGINEER: Concerned with all costs and resources used during production, the manufacturing engineer is going to pay attention to any metrics related to downtime, especially unplanned downtime (Figure 3.1). When an oven goes down, it’s usually not an easy fix. Beyond the cost of rework, when a reflow oven isn’t producing boards, it’s still consuming a lot of energy.

Line balancing is critical for effective energy usage; looking at oven utilization will let the manufacturing engineer know when it’s sitting idle (burning energy for nothing) and why it’s waiting for product: are the bottlenecks elsewhere on the line?

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