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Computers, lasers, and artificial intelligence are infiltrating every area of the PCB manufacturing facility. Over the last few years, most printed circuit manufacturers have invested heavily in integration of the complete shop equipment, controlled from one central computer mainframe. The interconnecting intelligence allows for quicker file processing, higher accuracy, and vastly improved yields.
One of the most expensive machineries is the laser direct imaging (LDI) system. There has been significant improvement in the accuracy, speed, quality, and reduction in overall manufacturing rejects. The new machines feature numerous cameras to locate the alignment holes, comparing them to the original Gerber file, and then digitally scaling the image to fit the panel. The newer laser imaging machines are capable of imaging down to 15-micron line widths and spaces.
From the beginning of a new PCB order, more powerful CAD/CAM manufacturing software is used to inspect the Gerber files, perform a design rule check, and identify any trace or hole violations that would result in shorts or opens later in the process. The new powerful software checks impedance throughout the circuit traces and layers. It adjusts for laminate shrinkage by calculating scaling and resizing each layer to compensate. The software will calculate etchback on traces and panelizes the job for maximum yield.
The software does not stop there. It coordinates feedback from post lamination alignment and X-ray drill, and adjusts each layer’s scaling in a database to ensure tighter layer-to-layer alignment. The software sends all the required information to the drills, routers, testers, imaging and any other machines connected to the company’s own internal network.
The biggest change has been the addition of lasers to many operations and machines—from laser drills that can sculpt through laminate to create blind microvias, to copper cutting/trimming lasers built into the automatic optical inspection units. These new lasers can easily remove small shorts. New technology even allows for 3D printing of copper to repair opens in a circuit, which greatly improves yields.
Computers are producing higher accuracy in alignment of inner layers by detecting errors in scaling of each layer with X-ray and then correcting the drilling files to correctly align the tooling holes for lamination and drilling.
Today’s drilling machines, vastly superior to machines of only a few years ago, are equipped with laser drill size measurement, broken bit detection, and massive drill canisters which automatically change bits according to wear or hit counts. The drills feature controlled depth drilling for back drilling of vias to reduce capacitance and improve impedance. Newer drills feature up to 250,000 rpm air bearing heads, and very high-speed drilling and very accurate table servos. In addition to normal mechanical drilling, manufacturers have laser drills. Powerful UV lasers cut through the copper and FR-4 material to drill tiny microvias one or two layers down, and thicker copper stop pads are used to halt the laser. Laser drilling is essential for HDI or very fine micro-PCBs required for today's microelectronics.
To improve inner layer drilling registration, X-rays look inside for special alignment pads and then find the best compromised location of the pads. The software then calculates for stretch or shrinkage in the panel’s size after lamination. They automatically adjust the drill file size by using scaling and drill alignment holes so the drill will more accurately hit the center of all pads. The machine will communicate to the drill unit, giving it new X-Y and offset stretch coordinates so it can increase or decrease the data file position and size of the panel to more accurately hit the center of all the pads.
Inkjet solder mask units eliminate the old inaccurate silkscreen method. The machine has multiple ink jet heads that quickly spray accurate lines, letters and drawings in white ink onto the finished solder mask. A powerful UV lamp dries and cures the ink as it sprays on the PCB. This eliminates the messy manufacturing of the silkscreen, the flip table, and the squeegeeing of ink onto the PCB.
Computers are now controlling the plating bath chemistry through constant monitoring and titrations. They sense a deficiency on one of the many chemicals and automatically add in the right amount to correct the bath during the run. The measuring and adjustment are all done in real-time. The chemical baths do not suddenly go out of specification, and important parameters such as copper ductility are well controlled.
Inkjet solder mask units have two different options. Older ones spray the entire board, which is then imaged with a laser direct imaging unit, developed, and then cured. Newer inkjet solder mask units apply and cure the solder mask ink with the openings for vias, directly onto the board. A powerful UV light then cures the solder mask right on the machine.
Computers in the lab allow for quicker cross-sections and easier spotting of potential problems before the boards are shipped. As well, the shop will have computerized tracking using bar codes or QR codes. The production manager can look at his computer identifying any job that is falling behind.
Newer flying probe electrical testing equipment is much faster. They feature many more little heads to probe each point on the printed circuit to test for shorts or opens. The improved speed and accuracy eliminate the need for older, fixed bed probe units.
Laser cutters for flex circuits quickly and very accurately, shape, scallop and cut the flex circuits, eliminating the old kick press and steel rule die method.
Cost saving is the goal. Even though a single direct imaging laser can cost well over a million dollars, a PCB facility lives or dies based on yields. In the past, a 70% yield was considered doing very well. Today with all the computer and laser assistance in manufacturing, most manufacturers are easily in the high 90% yield. This improvement goes directly to the bottom line. As well, it greatly reduces the dreaded re-run, which costs money and creates a delay in the delivery schedule to the customer.
This column originally appeared in the January 2021 issue of Design007 Magazine.