02-10-2012, 12:05 PM
PCB FABRICATION
PCB FABRICATION.docx (Size: 18.26 KB / Downloads: 23)
MEDIA
Art quality depends on both the output device and the media used. It is not necessary to use a transparent artwork medium as long as it is reasonably translucent to UV. Its fine less translucent material may need a lightly longer exposure time. Line definition, Black opaqueness and toner ink detention. It state flatter under laser printer heat then polyester or acetate film. Get the thickness you can find thinner stuff can. It should be rated at least 90gsm: 120gsm is even better but harder to find. It’s cheap and easily available from art suppliers.
OUTPUT DEVICES
Laser printers offer the best all-round solution. These are affordable, fast, and good quality. The printer used must have at least 600 pi resolution for all but the simplest PCB, as you will be usually working with multiplies of 0.06cm. 600 dpi divides into 40, so you get consist spacing and line width. It is very important that the printer for the PCB use do some test print on tracing paper to the blackest.
Even the best laser printers don’t cover large area as well. Always use manual paper feed and set the straightest possible paper output path to keep the artwork as flat as possible and minimize jamming. For small PCBs, you usually save the paper by cutting the sheet in half.
You may need to specify a vertical offset in your PCB software to make it print on the right part of the page. Some laser printers have poor dimension accuracy, which can problems in large PCBs. But as long as any error is linear, it can be compensated by scaling the printout in the software.
PHOTO RESIST PCB LAMINATIONS
Always use good quality pre-coated photoresist fireglass (FR4) board. Check carefully for scratches in the protective covering. You don’t need darkroom or subdued lighting when handling boards. As long as you avoid direct sunlight, minimize UV necessary exposure and developed immediately after UV exposure. In stagraphic microtrack boards quickly gives excellent resolution.
EXPOSURE
The photo resist board needed to be exposed to UV light through the artwork, using a UV Exposure box. UV exposure unit can easily be made using STD fluorescent lamp ballast and UV tubes. For small PCB’s 2-8W, 30.5cm tubes will be adequate.
If printer error has caused slight miss-registration, align the sheets to average the errors occur the whole PCBs to avoid breaking pad edges or tracks when drilling. When they are correctly aligned, staple the sheets together the opposite sides, about 10mm from the edge of the board.Forming a sleeve or envelope, the gap between the board edge and staple is important to stop the paper distorting the edge. Use the smallest stapler you can find, so that the thickness of staple not much more than of the PCB. Expose each side. After exposure, you can find a faint of the pattern in the photosensitive layer.
DEVELOPING
For developing a much better developer is silicate based product that comes as a liquid concentrate. You can leave the board in it for several times in the normal developing without any noticeable degradation. This also means that it is not temporary. Critically no risk at stripping in warm temperature. If the board is underexposed, you will get a thin layer of resist which isn’t removed by the developer. You can easily remove it by gently whip using a paper towel.
FETCHING
Ferric Chloride etching is a messy stuff, but easily available and cheaper than most alternatives. It attacts any material including stainless steel. So when setting area, use a plastic or ceramic sink, with plastic fittings and screws.
Copper water pipes may get splashed or dipped on. So sleeve or cover them in plastic. Adding a teaspoon of sail helps you to make the etching clearer and for easier inspection. With fresh hot Ferric Chloride, PCB will etch under five minutes. Fast etching produces better edge quality and consistent line width.
TIN PLATING
Tin plating a PCB makes it a lot easier to solder and it is pretty much essential for surface mount boards. Unless you have access to a roller tinning machine, chemical tinning is the only option. Uniformly, tin plate the board, either have the photo resist coating on most resists are intended to act as soldering fluxes or spray the board with network flux to prevent the copper from oxidizing at room temperature.
Tin plating crystals produces a good finish in few minutes. There are other tinning materials available. Some of them requires mixing with acid or high temperature ensure that the temperature of tinning solution is atleast 250C but not more than 400 C.
.DRILLING
If u have fiber glass board, you must use tungsten carbide drill bits, because fiber glass eats normal high speed steel bits very quickly. Although HSS drills are right for odd larger size(>2mm).Carbide drill bits are expensive and the thin ones snaps very easily.
When carbide bits below 1mm, one must use a vertical drill stand. You will break drills very quickly without one. Carbide drill bits are available as straight shank or thick (sometimes called turbo)sank. In straight sank the hole bit is the diameter of the hole and in thick sank drills are usually preferred because they are usually cheaper. The longer thin portion provides more flexibility.
SOLDERING
Soldering is the process of joining together of two metals to give physical banding and electrical conductivity. It is used in electrical and electronic circuit. Solder is a combination of metals at 180-2000C. To solder you need a soldering iron, a modern iron consisting of heating element, soldering bit, a handle and a power cord.
The heating element is either a resistance coil wounded a ceramic tube, or a thick film resistance element printed on ceramic base. The element is then in a metal tube for strength and protection. The heating element of soldering iron usually reaches temperature around370-400.The soldering bit is a specially shaped copper plated with chromium and iron. The plating makes it very resistant to aggressive solders and fluxes.
The commonly available solder is 63/37 that is 69%lead and 37% tin .It is also known as eutectic solder. The most desirable characteristics is that its solid state and liquid state, which occur at 3610C.Lead free solder are most costly and hardly to work.
Flex is an aggressive chemical that removes oxide and impurities from the part to be soldered. The chemical reaction at the point of connection is to take place foe metal to fuse.RMA type flux (Rosin Mildly Active)is the least corrosive of the readily available material, and provides an adequate oxide removal. In electronics a 60/40 fluxed core solder is used. Before soldering ,soldering points are cleaned and paste this flux. Before and after use whip the bit on a damp sponge. Always keep hot iron on a bunch stand when not in use.
PCB FABRICATION.docx (Size: 18.26 KB / Downloads: 23)
MEDIA
Art quality depends on both the output device and the media used. It is not necessary to use a transparent artwork medium as long as it is reasonably translucent to UV. Its fine less translucent material may need a lightly longer exposure time. Line definition, Black opaqueness and toner ink detention. It state flatter under laser printer heat then polyester or acetate film. Get the thickness you can find thinner stuff can. It should be rated at least 90gsm: 120gsm is even better but harder to find. It’s cheap and easily available from art suppliers.
OUTPUT DEVICES
Laser printers offer the best all-round solution. These are affordable, fast, and good quality. The printer used must have at least 600 pi resolution for all but the simplest PCB, as you will be usually working with multiplies of 0.06cm. 600 dpi divides into 40, so you get consist spacing and line width. It is very important that the printer for the PCB use do some test print on tracing paper to the blackest.
Even the best laser printers don’t cover large area as well. Always use manual paper feed and set the straightest possible paper output path to keep the artwork as flat as possible and minimize jamming. For small PCBs, you usually save the paper by cutting the sheet in half.
You may need to specify a vertical offset in your PCB software to make it print on the right part of the page. Some laser printers have poor dimension accuracy, which can problems in large PCBs. But as long as any error is linear, it can be compensated by scaling the printout in the software.
PHOTO RESIST PCB LAMINATIONS
Always use good quality pre-coated photoresist fireglass (FR4) board. Check carefully for scratches in the protective covering. You don’t need darkroom or subdued lighting when handling boards. As long as you avoid direct sunlight, minimize UV necessary exposure and developed immediately after UV exposure. In stagraphic microtrack boards quickly gives excellent resolution.
EXPOSURE
The photo resist board needed to be exposed to UV light through the artwork, using a UV Exposure box. UV exposure unit can easily be made using STD fluorescent lamp ballast and UV tubes. For small PCB’s 2-8W, 30.5cm tubes will be adequate.
If printer error has caused slight miss-registration, align the sheets to average the errors occur the whole PCBs to avoid breaking pad edges or tracks when drilling. When they are correctly aligned, staple the sheets together the opposite sides, about 10mm from the edge of the board.Forming a sleeve or envelope, the gap between the board edge and staple is important to stop the paper distorting the edge. Use the smallest stapler you can find, so that the thickness of staple not much more than of the PCB. Expose each side. After exposure, you can find a faint of the pattern in the photosensitive layer.
DEVELOPING
For developing a much better developer is silicate based product that comes as a liquid concentrate. You can leave the board in it for several times in the normal developing without any noticeable degradation. This also means that it is not temporary. Critically no risk at stripping in warm temperature. If the board is underexposed, you will get a thin layer of resist which isn’t removed by the developer. You can easily remove it by gently whip using a paper towel.
FETCHING
Ferric Chloride etching is a messy stuff, but easily available and cheaper than most alternatives. It attacts any material including stainless steel. So when setting area, use a plastic or ceramic sink, with plastic fittings and screws.
Copper water pipes may get splashed or dipped on. So sleeve or cover them in plastic. Adding a teaspoon of sail helps you to make the etching clearer and for easier inspection. With fresh hot Ferric Chloride, PCB will etch under five minutes. Fast etching produces better edge quality and consistent line width.
TIN PLATING
Tin plating a PCB makes it a lot easier to solder and it is pretty much essential for surface mount boards. Unless you have access to a roller tinning machine, chemical tinning is the only option. Uniformly, tin plate the board, either have the photo resist coating on most resists are intended to act as soldering fluxes or spray the board with network flux to prevent the copper from oxidizing at room temperature.
Tin plating crystals produces a good finish in few minutes. There are other tinning materials available. Some of them requires mixing with acid or high temperature ensure that the temperature of tinning solution is atleast 250C but not more than 400 C.
.DRILLING
If u have fiber glass board, you must use tungsten carbide drill bits, because fiber glass eats normal high speed steel bits very quickly. Although HSS drills are right for odd larger size(>2mm).Carbide drill bits are expensive and the thin ones snaps very easily.
When carbide bits below 1mm, one must use a vertical drill stand. You will break drills very quickly without one. Carbide drill bits are available as straight shank or thick (sometimes called turbo)sank. In straight sank the hole bit is the diameter of the hole and in thick sank drills are usually preferred because they are usually cheaper. The longer thin portion provides more flexibility.
SOLDERING
Soldering is the process of joining together of two metals to give physical banding and electrical conductivity. It is used in electrical and electronic circuit. Solder is a combination of metals at 180-2000C. To solder you need a soldering iron, a modern iron consisting of heating element, soldering bit, a handle and a power cord.
The heating element is either a resistance coil wounded a ceramic tube, or a thick film resistance element printed on ceramic base. The element is then in a metal tube for strength and protection. The heating element of soldering iron usually reaches temperature around370-400.The soldering bit is a specially shaped copper plated with chromium and iron. The plating makes it very resistant to aggressive solders and fluxes.
The commonly available solder is 63/37 that is 69%lead and 37% tin .It is also known as eutectic solder. The most desirable characteristics is that its solid state and liquid state, which occur at 3610C.Lead free solder are most costly and hardly to work.
Flex is an aggressive chemical that removes oxide and impurities from the part to be soldered. The chemical reaction at the point of connection is to take place foe metal to fuse.RMA type flux (Rosin Mildly Active)is the least corrosive of the readily available material, and provides an adequate oxide removal. In electronics a 60/40 fluxed core solder is used. Before soldering ,soldering points are cleaned and paste this flux. Before and after use whip the bit on a damp sponge. Always keep hot iron on a bunch stand when not in use.