... by fabricators because they're easier to work with and have smaller file sizes than positive layers. Remember, boards are manufactured en masse and must | CIRCUIT BOARDS | be stepped out into a panelized form. The result: Data sets with lots of unnecessary positive planes swell exponentially, bog down CAM systems, and crash | CIRCUIT BOARDS | photoplotters. After the basic prep work is completed, step into the fabrication analysis arena, where the game is one of checks and balances. You've got | CIRCUIT BOARDS | your design rules; fabricators have theirs. Checks and balances can resolve any conflicts between the two. Take soldermask layers, for instance. Often, these layers are | CIRCUIT BOARDS | not "intelligent" layers within a CAD tool; that is, there is not much in the way of capability checking within the tool. As a result, | CIRCUIT BOARDS | these are among the more troublesome layers for fabricators. The solution here is a fabrication analysis tool that can handle such issues as clearances, coverage, | CIRCUIT BOARDS | webbing, and so forth. For instance, most fab shops want the ...
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... cost. Two systems are particularly predominant: tin/silver/copper (SnAgCu) and, more recently, stabilised tin/copper (SnCuNi). Although the level of efficiency of both systems is not | CIRCUIT BOARDS | yet completely clear, the following presents the latest information: SnAgCu There is more experience in the field of silver systems. Here, differentiation is made between | CIRCUIT BOARDS | the Sn-3.5Ag-0.7Cu, Sn-4Ag-0.5Cu and Sn-3Ag- 0.5Cu systems which vary in use from continent to continent. However, the agreed expert opinion (IPC/Soldertech-Conference Brussels 2003) is that | CIRCUIT BOARDS | the technological differences between the three systems are negligible. Sn-3.5Ag-0.7Cu is the most common alloy in Europe. SnCuNi Although there are even fewer field results | CIRCUIT BOARDS | for the stabilised tin/copper system Sn-0.7Cu- 0.1Ni, it shows a lot of potential. It is called “stabilised” because the addition of nickel is said to | CIRCUIT BOARDS | show an improved hardening reaction in soldering. The creation of needle-structured crystals is said to alter to rounder ...
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... must be kept intact although the polyethylene packages capability of keeping humidity away is not really reliable. C STORAGE TIME The storage time of | CIRCUIT BOARDS | PCB`s should be as short as possible. PCB`s should be taken out due to the „first-in, first out“ rule. The the polyethylene packages should be | CIRCUIT BOARDS | taken away just before the assembling. Remaining PCB`s should be repacked again. To avoid exposure to draught, the packages should be stored in boxes. D | CIRCUIT BOARDS | SOLDERING TESTS PCB`s stored for over several months and being transported under questionable conditions, should be submitted again to a soldering test, being equivalent to | CIRCUIT BOARDS | your soldering process. E HEAT CONDITIONING OF THE PCB`S In any case we suggest a drying process of the PCB`s in a stove to reduce | CIRCUIT BOARDS | the moisture in the PCB`s to an acceptable minimum. Following parameters can be recommended: Drying time: C° 8 hours 120 10 hours 100 18 hours | CIRCUIT BOARDS | 80 Lower drying temperatures are also possible but need much more exposure time. We also suggest ...
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