Tips & Tricks: Machine Assist Time


Reading time ( words)

Assist time is the human intervention required to keep a machine producing during normal operation. It does not include errors, maintenance, setup, and prototyping.

Improving machine process throughput requires more or faster machines. Lost time on a machine can’t be recovered without adding more time. Consider an SMT printed circuit board assembly (PCBA) with 500 component placements: 

  • If a line is stopped for one minute, for any reason, and its capacity is 5,000 components per hour (cph) 
  • 83 placements are lost or four PCAs per 24 hours will not get shipped to the customer, likewise 
  • 40,000 cph = 667 placements lost or 32 PCAs per day
  • 100,000 cph = 1667 placements lost or 80 PCAs per day

There are many reasons for a machine to require assistance. PCB loading, stencil wiping, paste addition, feeder replenishment, and PCBA unloading—some require labor, some can be automated, but all will require some amount of time to complete. 

The pick-and-place (PnP) machine is usually the bottleneck. Let’s simplify and only look at three assist operations required of every PnP machine (see Table 1). 

Line A may be low volume; Line B, medium volume; and Line C, high volume. The maxi- mum achievable throughput would require instantaneous board transfer, registration and feeders of unlimited supply. 

Considering the PCBA above with 500 placements, assuming all the parts are supplied on tape and reel with an average reel size of 3,500 parts/reel, the resulting throughput based on Table 1 assist times can be seen in Table 2.

Table1_Horky_Feb2018.jpg

Table2_Horky_Feb2018.jpg

For comparison, the maximum achievable throughput can be seen in Table 3.

Table3_Horky_Feb18.jpg

As line throughput increases, assist time has greater impact and can justify increasing automation. 

How to Reduce Assist Time 

Print 

  • Use manual dispense guns with paste supplied in cartridges rather than scooping from jars 
  • Automate under stencil wipe and paste deposition 
  • Reduce stencil fiducial verification when possible 
  • Reduce auto post print inspection points when possible. Programming a single scan across the length of a board may suffice 

Place 

  • Improve operator’s response time to a machine request for assistance 
  • Purchase larger reel sizes, splice small reels into larger reels, multiply feeders’ positions 
  • Segregate panels with X-outs so you only search for bad marks when necessary 
  • Have extra feeders loaded and ready, so that many systems continuously report which feeder will run out next 

Reflow 

  • Automate handling, loading, and unloading 

In General 

  • Reducing operator assist time up and downline of placement will allow faster response to feeder replenishment 
  • Prioritize operator response for the bottle neck in your line 
  • Locate machines to reduce operator travel distance 
  • Increase conveyor speeds 

The numbers and calculations used here are greatly simplified. You can always create a simple spreadsheet with the assist variables you identify in your process for a better understanding of the impact on your throughput.

Share

Print


Suggested Items

More Than Inspection: It’s Process Improvement

01/09/2019 | Barry Matties, I-Connect007
Barry Matties speaks with Brian D’Amico, president of MIRTEC, about the current state of machine-to-machine communication in the industry, and how the inspection company is interfacing with the different manufacturing languages currently available to gather predictive data and feedback from every inspection step to eliminate future defects.

Challenges in Flex Circuit Assembly

12/19/2018 | I-Connect007 Research Team
In a recent I-Connect007 survey on flex circuits, we asked the following question: What are some of the challenges that you face utilizing flex circuits? Here are just a few of the replies, edited slightly for clarity.

SMT Electrolytic Capacitor Solder Joint Criteria and Integrity Investigation

12/21/2018 | David Hillman, Rockwell Collins
The body configuration of SMT electrolytic capacitors results in the solder joints being only partially visible for optical inspection purposes. Therefore, the use of adequate reflow soldering processes is critical for producing solder joints that are acceptable for their end-product use environment.



Copyright © 2019 I-Connect007. All rights reserved.