Design007 Magazine

Design007-Jan2021

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106 DESIGN007 MAGAZINE I JANUARY 2021 alignment. The software sends all the required information to the drills, routers, testers, imag- ing 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 opti- cal inspection units. These new lasers can eas- ily 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 cor- recting 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 capac- itance 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 mechani- cal 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 commu- nicate 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 manufac- turing of the silkscreen, the flip table, and the squeegee-ing 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 impor- tant 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 imag- ing unit, developed, and then cured. Newer ink- jet 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 prob- lems 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 equip- ment is much faster. They feature many more little heads to probe each point on the printed New technology even allows for 3D printing of copper to repair opens in a circuit, which greatly improves yields.

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