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SMT Line Balancing Worksheet: Find the Bottleneck Station

An SMT line is a chain, and the slowest link sets the speed. This worksheet lists every station with its cycle time and shows the bottleneck, line UPH and how balanced the line is.

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Seq	Station	Type	Cycle time (s) (s)	Station UPH	Boards per cycle
				150
				180
				116
				95
				133
				124

Total station cycle time

169

Fastest station UPH

180

Line cycle time (bottleneck)

In seconds, set by the slowest station.

Line UPH

94.7368

Balance efficiency

74.1%

Average station time divided by bottleneck time.

Balance loss

25.9%

Slack at fastest station

In seconds per board.

Station UPH is a stand-alone figure. The line runs at the bottleneck's rate. If a station processes a multi-board array, enter its cycle time per array and divide by boards per cycle to compare per board.

Bring line data into your ERP schedule

An optional review of linking measured cycle times to routings and scheduling.

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How to use it

Add one row per station in process order. Use measured cycle times from the machine logs or a stopwatch study, not nameplate values. Enter the station type so you can filter or sort. The station UPH is calculated for each row and the summary shows the line cycle time, line UPH, balance efficiency and slack. Edit values to simulate moving components between placement machines and see the effect.

Measure over at least 20 consecutive cycles
Convert array cycle time to per-board time before comparing
Record the product and program version the times belong to

The metrics

Line cycle time equals the longest station cycle time. Line UPH is 3600 divided by that. Balance efficiency is the average station time divided by the maximum, so a perfectly balanced line scores 100 percent. Balance loss is the remainder. A low score means stations are idle waiting for the bottleneck, which is often the best place to shift work, for example moving parts from a slow placer to the chip shooter.

Common mistakes

Do not confuse machine rated speed with achieved cycle time, which includes board transfer, vision and nozzle changes. Reflow conveyor pitch limits throughput and is easy to forget. Dual-lane machines and buffer conveyors change the effective cycle, so model them carefully. Finally, a balanced line that is still slow means the whole line needs more capacity, not more balancing. Use the placement rate calculator to size machine counts.

Frequently Asked Questions

What is line balancing in SMT?

It means distributing work across machines so cycle times are as even as possible, reducing idle time at faster stations. In SMT this usually means reassigning component placements between machines to equalize each machine's program time.

How do I find the bottleneck station?

It is the station with the longest cycle time per board. In this worksheet it is the row with the highest cycle time, and the summary reports it as the line cycle time.

What is a good balance efficiency?

Above 85 to 90 percent is generally considered well balanced for a placement section, though printers, ovens and inspection machines rarely match placement time exactly. Use the number as a trend, not a single target.

How does array size affect cycle time?

Arrays raise the per-cycle time but spread the transfer and fiducial overhead over several boards. Enter the cycle time for the whole array and compare stations on a per-board basis to find the real constraint.

Netray can collect station cycle times from your MES or machine logs and surface bottleneck trends against ERP work orders.

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