THE ABILITY TO efficiently manufacture a product has driven the electronics industry toward automated processes and streamlined production facilities. Despite this, the need for hand-soldering operations remains an integral part of most manufacturing processes. Whether it is the need to attach a large connector, conduct a field modification, or to rework a noncompliant item, hand-soldering operations require personnel with the proper skills to complete the job. The use of proper, well-maintained equipment is paramount to completing the task in a timely manner, while maintaining a high level of quality.
The machines that laser-cut SMT stencils use gantries and motion controls similar to those in pick-and-place machines. Moving parts wear, and machines drift out of spec if they are not regularly maintained and calibrated. The opportunity to create apertures that are out of position, incompletely cut, or obstructed with slag happens every day. And while electro-formed foils might eliminate the stencil cutter as a variable, they introduce other factors: their size and positional accuracy are only as good as the artwork used to form them, which depends on the artwork's photoplotter - another machine full of moving parts. Additionally, the nature of the plating process subjects these foils to regular variations in thickness that introduce error into area ratio estimates.* First, wipe the tip on a clean, slightly damp sponge to remove oxidation and excess solder. A coiled brass wire pad can also be used to remove excess solder.* Replace sponges at regular intervals when they become dirty. Replacement sponges are inexpensive, and this simple practice will help avoid introducing contaminants.Why has stencil verification become optional and what drove it to the brink of extinction? Likely a combination of efficiency and economics. Basic stencil verification procedures use a negative image of the stencil pattern, a light source and a human to verify the presence of all desired apertures and measure a few of them. As aperture counts increase and sizes decrease, the efficacy of human inspection techniques becomes questionable, and coordinate measurement machines (CMMs) are needed to meet measurement speed and accuracy requirements.* The solder should be fed to the connection, not to the tip. Once a heat bridge is established, the connection will melt the solder and the solder wire should be moved around the connection to ensure adequate coverage.* Select the lowest tip temperature needed to facilitate solder reflow. The correct temperature depends on the type of solder alloy being used. Pb-free alloys have higher melting points than SnPb alloys, and often have a frosted or grainy appearance (in the final connection). A grainy appearance on a SnPb connection is a clear indication that the tip temperature is too high. If a connection is being made on a multilayer board with an internal ground plane, the ground plane acts as a heat sink. Auxiliary heating is needed to overcome the heat sink effects.Learn about http://www.homemadesolarpanelsreview.net/ and how to reduce your energy bills by 80% or more. Visit http://www.homemadesolarpanelsreview.net/ to learn more now!If you decide to begin building you own home made solar panels you want to have all the needed parts such as photovoltaic cells, copper wire, boards, glass and all the other needed tools including a soldering iron that heats up fast. You want take care as the markets are full of non-quality solar cells, the most cost-effective and best ones can be found online. Basically you won't be spending more than one hundred and fifty to two hundred dollars altogether. Imagine that a solar panel normally costs around $3000.What's the probability of getting a stencil with apertures out of spec? Assume the stencil vendor has the highly touted Six Sigma quality in his process. Most are in the sub 5-Sigma range, assuming Six Sigma makes for conservative estimates and easy math. Allowing for the 1.5[SIGMA], shift, the supplier creates 3.4 defects per million opportunities. Consider stencils with 10,000 apertures: 100 stencils represent 1,000,000 opportunities. Even at a Six Sigma level, between 3 and 4 of each 100 stencils will have a manufacturing defect. Think about how many stencils are regularly used in production. How many defects are out there right now, waiting to get installed in an assembly printing process?No matter how many home made solar panels you need to make, building them on your own will drastically reduce the costs comparing to what you would pay for some pre-made ones. And if you're a bit lucky you might be able to get some of the materials at a local garage sale. You can save more than 80% on your energy bills each year by making your own solar panels.* When soldering, do not apply downward pressure on the joint being soldered. Simply rest the tip of the iron on the joint to help establish a heat bridge. (A small bead of solder on the tip will also aid in forming a heat bridge.) Downward pressure will not aid in solder reflow. It will, however, cause undesired mechanical stress on the connection area and may result in lifting the pad.* Finally, always turn off equipment when not in use, and never use tips for purposes other than intended. Breaks or cracks in the plating that result from improper tip use will drastically reduce its lifespan, or at the very least, interfere with its heat transfer capabilities.Au.: SPI systems can be used for a variety of other stencil-related tasks, including vendor qualification, aperture design guideline assessment, and foil material evaluation.
ACI TECHNOLOGIES INC. (aciusa.org) is the National Center of Excellence in Electronics Manufacturing, specializing in manufacturing services, IPC standards and manufacturing training, failure analysis and other analytical services. This column appears monthly.
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