The objective of this project was to develop a Lean Manufacturing Line for a customer to build 21 different products consisting of three families, for After Market White Goods. This project was a personal award winning project from the vendor. The volume of this production line was considered to be of moderate volume of 200 to 500 boards per day for each product. Consideration was given for the occasional repair product required immediately, thus requiring a line that could provide lot size 1. These changeovers from one product to the next would be automated to the extent possible. It was important to minimize the amount of set up performed, thus removing the potential for error. The amount and type of automation was given careful consideration, providing ease of troubleshooting. It is easy sometimes to automate for the sake of technology.

The beginning of the production line started with a conveyor called a de-stacker. There were two de-stacker units on each conveyor containing up to 200 (2-up) printed circuit boards. The 2-up panel was established to have a common size or form factor to minimize line and machine setup. Each panel contained a carrier strip on the top and bottom to provide the difference in width between each product type and a location on the bottom strip for a bar code label.

When a new stack of printed circuit boards were loaded into one of the de-stack units, it was sensed that a new stack was just loaded. The operator would verify the silk screen part number on the printed circuit board matched the paper work. The part number was then scanned from the bar code on the paper work into SQL Database. When the first panel would be unloaded on to the next step in the assembly process to attaché a printed circuit board label to the bottom carrier strip, at the same location every time. The first board would stop at a buffer before the label applicator would apply the label. A light tower would be lit to inform the operator that was the first board loaded and to verify the product loaded in the de-stacker was the same product id on the label,( in code 128 ), to be applied. When this was accomplished, then the line would run automatically from this point forward until the stack of printed circuit boards was depleted. After the label was applied, the printed circuit board moved into a verification station to make sure that the label was readable. If the label failed, a light tower would light and an operator would remove the printed circuit board panel from the line.

In front of the screen printer was a buffer area containing a bar code reader connected to the PLC in the conveyor. When a new product was ready to enter into the screen printer, the printed circuit board would stop and a light tower turned on. Operator would then change out the stencil on the screen printer. Auto paste dispense on the screen printer minimized the amount of time spent placing solder paste on the stencil. Auto inspection of the solder paste was accomplished using an Optical Inspection in-line unit after the screen printer for first article. When the proper deposition of solder paste was accomplished the operator would then let the rest of the batch of boards enter into the screen printer. One of the driving factors for the reliability of the line was to control the amount of solder paste. If the process was stable and the amount of solder paste consistent on the printed circuit board, then the manufacturing process would remain stable. The surface mount components packages were larger then electrically required to avoid any miss pick or misplacement issues.

The next step in the process was the placement of surface mount components and a few odd form connectors. Eliminating setup was the main driving factor in this project and this was accomplished by using two single head high speed chip shooter surface mount placement machines and one pick and place surface mount placement machine for connectors and a few large active devices. The driving factor for the number of machines was the number of components to be placed for the 21 different products. The common component feeder setup was optimized on the machine, based on the total production requirements and allowing for 20% empty feeder space. Consideration was given to create a pull system for each machine as best possible and still maintain machine utilization. When a new printed circuit board would stage in front of the first surface mount machine, the bar code would determine the product ID, automatically change the machine program and when the program was changed, SMEMA signals would allow the board to enter into the machine for population. This was accomplished for each of the three surface mount machines.

Reflow oven process was the next step in the manufacturing process and was able to accomplish a common reflow oven profile for each of the 21 different products. Thus, no secondary automation or setup was required in this step of the manufacturing process.


Printed circuit boards proceed then to the testing area consisting of three perpendicular lines off from the main assembly line and downstream from surface mount placement. Testing was based on performing an ICT (In-Circuit-Test) for each family of product, thus the three process lines for test. Each tester was configured with a common test fixture to handle all of the products within each family. Printed circuit boards were directed to the appropriate test line via their bar labels. A turn unit conveyor’s PLC controller was connected to the bar code readers. Each product name within the respective family was located within a table and as each product came down the line it was checked against the table at each turn unit. This provided the lot size one capability, although the line was generally run with 200 to 500 boards of the same product. Defective printed circuit boards were automatically removed from the test line and good product returned to the main manufacturing line via a common return conveyor.

Final assembly for this product was fairly simple, consisting of a few standalone work stations, semiautomatic equipment for blister packaging, adding some hard ware, some primary pack and secondary pack. Three final assembly line conveyor stubs were setup via the family of product being completed. There were directed via a bar code reader connected to a turn conveyor unit to direct the product to the correct line.


The printed circuit board design was in a panel format, divided into circuits of 4 X 6 for the key fob product. The panel layout was 4 circuits in “y” machine plane and 6 circuits in the “x” machine plane. The overall panel size was 5.1” in the “y” machine plane and 6.6” in the “x” machine plane. Each circuit was partially routed at the printed circuit board manufacture. It was important not to over route each circuit, causing sag on the conveyor belts during transport from one process to the next. These partially routed circuits were totally routed from the panel after ICT testing was completed.

The receiver panel was a two up panel, with overall dimensions of 6.3” wide in the placement “y” machine plane and 8.4” long in the “x” machine plane. The receiver would eventually end up in the garage door opener itself. The receiver circuitry was more complex then the transmitter and used more odd form type components like coils, relays, connectors and through-hole electrolytic capacitors. The receiver printed circuit board manufacturing line was similar to the transmitter production line.

I wanted to review a couple of items that most production engineers take for granted, but can really make a difference to the reliability of the production line. Connectors and some other odd form parts were sourced and purchased in China. The placement of these parts was terrible. The pocket within the tape was too small for the connector part, so with normal tolerance, some parts would stick in the pocket of the reel tape and cause a miss-pick. We went back to the Chinese supplier and specified the pocket dimensions, appropriate for the part. Clearance specified was .008” - .010” between the connector side walls and the side walls of the reel tape. The EIA specifications for pocket clearance are larger and can allow parts to shift in the pocket, causing miss picks. Some surface mount connectors came with pick tabs for vacuum pickup and some connectors required custom grippers. Grippers were used on some connectors that would not sit in a tape pocket or have a vacuum pickup location. Custom grippers were developed for the surface mount equipment. This required a special pocket with a shelf in the reel tape for the connector to rest on and keep the connector oriented in the proper position for machine pickup. The clearance for the grippers was .020” on either side of the connector side wall of the tape pocket.

Vision inspection, after component placement, on the transmitter process line was determined unnecessary. Component chips were 0603’s, moving to 0402’s, it was determined the accuracy of the machine and component pad design were adequate to reliably place the components. A manual visual AQL inspection of the printed circuit board could be done, at this step in the process. If there were to be any problems in the process, it was determined it would occur after the reflow process, because of inadequate paste distribution or too much paste on the surface mount pads. Vision inspection was introduced into the system after reflow, providing the best solution to any quality issues for placement errors. Although, this position in the assembly process was the most expensive to repair, the amount of defects would be extremely small, it was cheaper to remove them from the system and through them away. Defective circuits within the panel were marked with a white ink dot. This allowed them to be sorted and removed further down the process after de-paneling.

The reflow process for the transmitter product was very stable, because the panel and circuit boards did not change. The mass of the product going through the reflow oven was consistent, thus no adjustments were required for conveyor speed, air flow or temperature settings.

Printed circuit panels moved from the reflow process into a programmable buffer. This buffer acted as inline control of the production line. The buffer was programmed to store a preset amount of printed circuit boards and then shut down the input to the reflow oven by shutting off the SMEMA signals. Using Lean or pull manufacturing techniques, the downstream final assembly was faster then the surface mount portion of the assembly line. When stoppages occurred, they would clear themselves after the problem had been addressed. The FIFO buffer allowed the printed circuit boards coming in from the oven to accumulate in the buffer for a predetermined amount of time to cool. This provided a consistent temperature for the printed circuit boards entering the vision inspection system, but more important the ICT (In Circuit Tester) that followed. Having consistent low temperature readings, the chip and wire bonds were more stable in test. Both ICT and Vision Inspection allowed for a faster process time then full functional testing, especially when the down stream process steps needed to be slightly faster providing for a pull system.

The next step after test was to de-panel the circuits. With the panel being partially routed, the final routing process removed the short tie stub holding the circuit to the panel. Special grippers would hold four circuits at a time in the “y” machine plane and after cutting the tabs, would hold all four circuits, until the last circuit was cut. Then all four were dropped on to a flat belt conveyor, where each circuit was clamped and held by custom tooling for a Cartesian Robot to pick up all four circuits at one time. A pallet holding plastic bases of the key fob were moved into position for the robot to place each circuit into the base, using a four headed vacuum pickup end effectors. Plastic bases contained 4 locking latches so when the circuit was pushed into the base, it was latched into place. Plastic bases contained a chamfer of .100” at 45 degrees around the outside perimeter, were previously loaded into the pallets in a Cartesian robot operation. This allowed the circuits to be reliably inserted into the base without vision to guide the robot. The positioning accuracy of the robot was .003”. Pallet fabrication was done using a machine able plastic. The plastic pallet was routed to the maximum plastic key fob base tolerance, plus .002”, with a .003” nominal tolerance. Key fob pockets on the pallet contained lead in edges of .100”.

 Pallets containing 24 circuits moved from inserting individual circuits into the bases, to the next position in the final assembly process. The final assembly process was an oval architectural configuration using roller chain, with position stops for each assembly step in the process. The final assembly oval conveyor with robotic stations along the conveyor ran perpendicular to the back end of the surface mount line. The pallet was located using pneumatic locators at each step in the process. The locators used a cone style pin inserted into a .250” round hole. The second locator also used a .250” hole, but was elongated in the machine x plane. This assured the location of the pallet in reference to the robotic placement points. The next step in the process was to insert the circular watch battery into a spring clip. The packagings of components were as important to the assembly process, as the robot assembly itself. The batteries were loaded at the supplier into tubes that could be fed into a multi tube stick feeder. The batteries would slide down a custom machined slide for robotic pickup. The feeder could handle a stack of 15 sticks and each stick could handle 80 batteries. With this inventory of batteries on the assembly line, little operator intervention was required. Process time at this stage of the assembly was getting progressively faster to maintain the integrity of Lean and JCIT manufacturing. Multiple feeders were placed at each cell to minimize part handling and to assure placement reliability.