Ipc Sm 840 Solder Mask Pdf Download
Melva Simons
It seems that, when the solder mask is on the "pin" class, Allegro can associate it to a specific net, so it won't report any error when a same net shape or via is too close or even overlapping, this is alright. But when it comes to the solder mask on the "package geometry", Allegro cannot do that, so it will report DRC warnings.
Soldermask is not "net" related - hence there are soldermask DRC's. What exact DRC are you seeing? Can you post a picture or a board file. You can add soldermask on a pin or under board or package geometry and the soldermask drc system will check for these depending on the rules you set.
OK - so the soldermask defined for on the pin is the same pin so I wouldn;t expect to see a DRC here anyway. The first picture you are overlapping a pin with a soldermask shape so the DRC makes sense.
Solder mask, solder stop mask or solder resist is a thin lacquer-like layer of polymer that is usually applied to the copper traces of a printed circuit board (PCB) for protection against oxidation and to prevent solder bridges from forming between closely spaced solder pads. A solder bridge is an unintended electrical connection between two conductors by means of a small blob of solder. PCBs use solder masks to prevent this from happening. Solder mask is not always used for hand soldered assemblies, but is essential for mass-produced boards that are soldered automatically using reflow or wave soldering techniques. Once applied, openings must be made in the solder mask wherever components are soldered, which is accomplished using photolithography.[1] Solder mask is traditionally green, but is also available in many other colors.[2]
Solder mask comes in different media depending upon the demands of the application. The lowest-cost solder mask is epoxy liquid that is silkscreened through the pattern onto the PCB. Other types are the liquid photoimageable solder mask (LPSM or LPI) inks and dry-film photoimageable solder mask (DFSM). LPSM can be silkscreened or sprayed on the PCB, exposed to the pattern and developed to provide openings in the pattern for parts to be soldered to the copper pads. DFSM is vacuum-laminated on the PCB then exposed and developed. All three processes typically go through a thermal cure of some type after the pattern is defined although LPI solder masks are also available in ultraviolet (UV) cure.
In electronic design automation, the solder mask is treated as part of the layer stack of the printed circuit board, and is described in individual Gerber files for the top and bottom side of the PCB like any other layer (such as the copper and silk-screen layers).[4] Typical names for these layers include tStop/bStop aka STC/STS[5][nb 1] or TSM/BSM (EAGLE), F.Mask/B.Mask (KiCad), StopTop/StopBot (TARGET), maskTop/maskBottom (Fritzing), SMT/SMB (OrCAD), MT.PHO/MB.PHO (PADS), LSMVS/LSMRS (WEdirekt)[6] or GTS/GBS (Gerber and many others[7]).
So if you use the command Tools - Padstack - Modify Design Padstack then click on one of the pads that is missing mask then right click - Edit, Padstack Editor will launch and you can add a definition for soldermask. Even if you copy the design pad size so it's one for one. Once complete use File - Update to Design and Exit and this then updates the padstack in the board file with a mask definition. Continue working through the pads that need this. The ideal scenario is that you edit the actual library padstack so that next time you use this padstack it has been updated to suit.
So soldermask is an opening, you define an opening in padstack editor for items that you don't want soldermask on. When you send this to the fabricator he makes a negative of this to create a soldermask film, they then print soldernask on the board leaving your pins clear of soldermask (if that makes sense). Vias - depends, sometimes users want these covered with mask sometimes not, sometimes only one side. You may also need to generate a pastemask (where solder is printed on the pads) for automatic assembly. Hope that helps
The soldermask is a negative of the resulting film. This means anything you draw on it will represent holes in the solder mask. (typically pads have soldermask enabled -> means there will be a hole in the mask with the same size as the pad.)
Now, if you want all the copper on the bottom side to be exposed so it gets an extra layer of solder during a reflow operation (or manually if hand-soldered), you should explain that to your vendor. (Sometimes board designers will intentionally leave power traces uncovered by soldermask to allow solder to build up the thickness of the trace to increase the current carrying capacity.)
If your board fabricator requires a Gerber file showing where soldermask SHOULD be applied, then KiCAD can not produce the file. Find a different board fabricator. Like @bobc said in Post #12, there are dozens of fabricators who can use the Gerber files produced by KiCAD with the options shown in Post #10.
After PCB fabrication, the copper traces on the board typically face the risk of oxidation and corrosion due to environmental exposure. The most reliable way to prevent this and increase the life of the PCB is to provide a protective coating known as a solder mask layer.
Solder mask is a thin layer of polymer that is put on a circuit board to protect the copper from oxidation and shorts during operation. It also protects the PCB from environmental influences such as dust and several other contaminants that may lead to shorts in the long run.
These are typically used by engineers to identify openings in the green solder mask, already applied on the PCB. This particular layer of solder mask is added through epoxy or film methods. Next, the component pins are soldered to the board utilizing the openings that have been registered using the masks.
The traces on the top-side of the board are called top traces and the corresponding solder mask used is called a top-side mask. Identical to the top-side mask, the bottom mask is used for the bottom side of the board.
The most cost-effective option among solder masks is epoxy. It is a polymer that is silkscreened on the PCB. Silkscreening refers to a printing technique that uses a woven mesh to support ink-blocking patterns. The mesh enables the open areas to be identified for the process of ink transfer. This step is then followed by thermal curing.
LPI solder masks are actually a mix of two distinct liquids. These liquids are kept separately and mixed right before the application of the mask layer to enable longer shelf life. LPI is also one of the more cost-effective options among various other types.
LPI is employed for curtain coat, screen printing, and spray applications. This mask is a blend of various polymers and solvents. A thin coating can be formed using this mask that can stick to the target area surface. After using this mask, the PCB will generally not require any final surface finish that is currently available.
Before mask application, the panels are subjected to cleaning and are checked for any sign of oxidation. This is done using a chemical solution, aluminum oxide solution, or using suspended pumice to scrub the panels.
One of the most popular techniques used to expose the panel surface to UV light is through the use of film tools and contact printers. The top and bottom sheets of the film are printed using emulsion to block areas that need to be soldered. Production panels and film are then fixed in position, making use of tooling on the printer and exposed to a UV light source simultaneously.
The use of dry film photoimageable solder masks requires vacuum lamination. This dry film is subjected to exposure and then developed. Post-development, openings are identified to generate a pattern, after which the components are soldered to the copper pads. High-density wiring boards benefit most from dry film solder masks as it does not flood the through-holes.
Regardless of the PCB solder mask types used, the resulting mask will leave behind certain exposed areas of copper on the circuit board. These exposed areas need to be plated with a suitable surface finish to prevent oxidation. One of the most popular surface finishes available is hot air solder leveling (HASL). Depending on the requirement other surface finishes also can be used such as electroless nickel electroless palladium immersion gold (ENEPIG) and electroless nickel immersion gold (ENIG). When needed, additional holes in the mask layer are left for the paste mask. This paste mask is utilized to attach pads or other components to the board based on the manufacturing process used.
Tenting vias is a popular process used to protect PCBs and is chosen over epoxy filling or mask plugging due to cost considerations. Within methods of via tenting, liquid photoimageable (LPI) solder mask tenting is most cost-effective. To ensure a better tented via you can also use resin filling which is higher in cost.
Solder mask clearance is a tolerance to decide how close the solder mask can be to the PCB surface features. The purpose of this tolerance/clearance is to provide adequate spacing known as solder dams between surface features that receive solder. This prevents the formation of solder bridges.
Solder mask defined pads are those where the mask opening is smaller than the copper pad such that the solder mask will define the size of the pad used in BGAs. Changes in the mask clearance will decide the copper pad size.
The solder mask process needs fitting tolerances to be considered such that the mask clearance should always be greater than the solder pads. This is required to keep the whole pad free of solder resist and ensure optimal soldering as per the new H revisions.
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