In the last few years, the electronics industry has seen some truly amazing advancements in technology. Devices and components we take for granted every day have become smaller, faster and significantly smarter. These new devices have given our lives a science fiction sort of aura. We now do things daily that were part of the imagination of sci-fi movie writers. During this time, assembly technology has grown at a steady pace with a few big improvements, mostly to processes and machinery. While PCB manufacturing has seen a significant number of major game changes in processes, the major improvements seen in assembly processes are based on smart vision systems and large computing power, giving the machinery a sort of artificial intelligence.
PCB manufacturing has grown along with many extreme advances in the process technology as well as the machinery. An expensive but indispensable digital direct download laser imaging unit decreases line widths, eliminating photo tools and developers. The high-resolution laser exposure unit increases yields, measures scaling differences, and then compensates for them and increases throughput.
Another big invention for PCB manufacturers is the laser drill. The 45-micron beam can ablate copper and FR4 producing very small, accurately placed HDI micro vias. The switch by many high-volume manufacturers to HDI is responsible for decreasing the PCB size and the number of components per side. Newly designed drilling machines now have much higher speeds, up to 250,000 rpm, which enables drilling with smaller bits. Many drills now come with Z-axis control, which allows back drilling and decreases node impedance; this enables drilling holes as small as three mils.
Shop floor improvements have resulted from smart barcodes and RFID systems to track the assemblies as they pass through the plant. Newer laser soldering robots with a variable diameter laser beam optimize energetic conversion into heat. The laser pinpoint soldering has features such as multi-directional soldering round components, which eliminates most part interference. New multi-ganged six-axis robots, with human-like hands and dexterity, perform various manufacturing applications including insertion, wiring, assembling, adhesive application, soldering and labeling. Human motion is imitated through the use of guided, intuitive machines. The result is a process very close to human assembly. Further improvements to PCB production are achieved by embedding components between the laminated FR4 layers. These small components are soldered to a sub-PCB and then assembled into the PCB during lamination, further increasing the density required by the small electronics that we use every day.
Lead-free solder has been a major and challenging aspect of technology for the PCB assembly industry to overcome. It took some time to perfect, as the reflow temperature was a much higher 260°C, causing increased solder dwell times with corresponding lower yield ratios. The improved computer technology in the new assembly machinery has enabled assemblers to cut costs while increasing yields through better feedback and smarter operator interface systems. Improvements in under fill adhesives, better conformal coatings and smarter IR and vapor phase reflow machines have offered increased yields as well as enabled the assembly of more exotic new fine-pitch components. Where older pick and place machines were finicky when trying to place smaller chip components, newer pick and place machines use state of the art vision cameras coupled with intelligent computers that can identify and properly locate even the smallest part. Even older machines are getting new upgrades to the software, cameras and computer power, making operations more autonomous while improving yields.
One big improvement to PCB assembly has been in applying the solder paste with ink jet technology. The ink jet replaces the expensive stencil and allows for changes on the fly. The recent push in ink jet technology abilities created ink jet solder machines, which print the solder paste directly onto the PCB with smaller features. The solder paste ink jet eliminates photo tools and silkscreen frames.. Similar inkjet technology can directly image units using a removable etch resist directly on the inner layer or PCB surface. This eliminates the dry film lamination process completely.
These advancements in technology not only help with the manufacturing of PCBs, but also the testing of the finished product. A major improvement in automatic inspection with X-ray vision systems has allowed assembly companies to refine procedures involved in placing and reflowing large BGA components that suffer from voids in the solder balls. The new automatic inspection units feature automated programming with multiresolution programs and advanced processing for image quality, 2D and 3D slice image extraction and X-ray tubes with adjustable output to increase definition tracks and capture defects as transferred by receiving data from automatic optical inspection (AOI) units. Significant improvements have evolved in AOI with improved imaging of spotting smaller features. Displayed are enlarged images at high resolution that offer both a top and angled view provided by a CCD camera. This makes the process of decision making much simpler because of the additional information provided to the user. The AOI units also now contain a very precise laser ablation knife system used to remove shorts and extra copper after etching.
Quality control tools have also been improving. High-speed flying probe electrical testing with smarter computers and advanced imaging capture are coupled with bulk electrostatic pre-testing machines with thousands of probes. The bulk tester then talks to the flying probe electrical tester, telling it which nodes are okay, eliminating 80 percent of the flying probe testing time. New cam software is constantly being upgraded for advanced layer scaling by interconnecting and transferring scaling information from the X-ray panel drill. The new software has the ability to calculate inner layer impedance for high layer count boards and helps improve HDI production. The software creates easier PCB panelization, adding the ability to run multiple jobs on one panel. Just like assembly machinery, the PCB industry machines are getting smarter, making production and product testing faster than ever. These advancements are creating an increase in yields as well allowing for more complicated PCBs, driving us ever closer to our every sci-fi fantasy.