Secrets for Mastering the Art of Choosing the Right Solder M

2020-01-15 10:48Writer: qyadminReading:

solder mask pcb 

       What is solder mask in PCB?  Soldermask is a protective layer of liquid photo image able lacquer applied on the TOP. and BOTTOM side of a Printed Circuit Board. The function of the Soldermask is to protect the copper, apart from the solder pads, from:
 
solder mask creating shorts during soldering (bridges)
solder mask creating shorts during operation due to external conductive influences
solder mask creating shorts during operation from net to net due to high Voltage spikes
environmental influences like dust and other contaminations. that may create shorts in the long run
The Soldermask is first printed. or sprayed on to the production panel. and then UV-exposed with the correct solder mask pattern, developed and dried. Soldermask is usually green but can also applied as: black, blue, white, red, clear. Look here to see how it done in production.
 
 
      Most , the solder mask keeps the solder on the pads, as opposed to flowing onto traces, planes, or empty board space. This reduces the likelihood that solder. will form bridges (unintended connections) from one element to another. Solder masks are critical for wave soldering, which is a mass production technique. But, solder masks also make hand soldering faster, easier, and more accurate.
 
      In the photo below, the green coating is the solder mask. See how the solder mask coats the entire board except for the pads. The pads exposed to allow you to solder parts to them.
 
      Usually, you don’t need to do anything in your PCB software to enable the solder mask. The software makes holes in the mask that correspond to pads. Additionally, the Copper Connection application grows those holes by default. so that moderate manufacturing misalignment (registration error) won’t overlap the pads.
 
  A lot of the space on the PCB occupied by the solder mask. Solder mask is actually a resin-based covering. that protects your PCB from contaminants and oxidation from exterior resources. such as manual managing, manufacturing digesting and environmental results. , the solder mask would cover every area of your table aside from drill openings. and footprint pads. But in practice, there is a tolerance that limitations. how close the solder mask is usually to surface elements. This tolerance recognized as solder mask clearance. and identifying the right tolerance specs for your PCB design. can impact your board’s manufacturability. Let’s have a closer take a look at solder mask clearance. especially of its effect on the PCB assembly process. to work with you to make the right options for your PCB design.

solder mask thickness

 
        The typical solder mask thickness (perpendicular to the board) is at least 0.8 mils. Solder mask will be thinner near the edges of traces and can reach as thin as 0.3 mils or less. In general, you'll want about 0.5 mils of solder mask over your traces.
 
On conductor side edges : > 7 micron (t1).
On conductor top : > 7 micron (t2).
Maximum Soldermask thickness can be up to 40µm for 35µm finished copper thickness. For higher final copper thicknesses, the Soldermask thickness can be up to 80µm
 
The Soldermask may encroach on lands. as long as the minimum annular ring requirements maintained.
Soldermask permitted in those PTH not intended for solder fill.
No isolated pads exposed.
No Soldermask encroachment on edge board connector fingers or test points.
On SMT-pads with pitch 1,25 mm encroachment permitted on one side of land only and does not
exceed 50 micron (2 mil).
On SMT-pad with pitch < 1,25 mm encroachment permitted on one side of land only and does not
exceed 25 micron (1 mil).
When you order silkscreen, you almost always get solder mask on both sides as well. Solder mask (or soldermask) is a coating. that protects the circuit from corrosion and electrical shorts. It also provides electrical insulation. that allows higher voltage traces to placed nearer to each other.

dry film solder mask

 
      Dry Film Solder Mask negative working, 75 Micron Thick. Application of a Dry Film solder mask (DFSM). gives the Printed Circuit Board (PCB) fabricator. Dry Film Solder Mask negative working, 75 Micron (3 Mils) Thick (A 40um thick version. is available by request). Application of a Dry Film solder mask (DFSM). gives the Printed Circuit Board (PCB) fabricator the  advantages
 
      This Dry Film Solder Mask (DFSM) is an aqueous processible. dry film photopolymer solder mask. utilizing epoxy chemistry materials well known for their electrical insulation. chemical resistance and dimensional stability properties. 
 
      This Dry film Solder mask is a transparent, high gloss forest green material. which  supplied in thicknesses of 75 microns (3mils) . Like most other dry film products. the photopolymer  sandwiched between a 25 micron(1.0mil) polyester support sheet. and a 25 micron (1mil) polyethylene release sheet..
 
      This DFSM will withstand most solvent and aqueous defluxing media. Due to the Dry Film Soldermask  high resolution characteristics. straight sidewall via holes tenting. chemical and thermal resistance properties. the DFSM product is  suited for use on high density surface. mount technology (SMT) printed wiring board designs. This DFSM  designed for use on rigid printed wiring boards. and is not recommended for use on flexible circuits.

solder mask dielectric constant

 
       solder mask dielectric constant is 3.3 to 3.8. For example, in contrast to circuit laminates intended for RF/microwave applications. and often characterized at 10 GHz, the typical dissipation factor (Df) of an LPI solder mask is 0.025 at 1 GHz. with a dielectric constant (Dk) of around 3.3 to 3.8 at the same frequency, depending upon formulation
 
 

  Solder Mask Clearance

 
  PCB assembly, the procedure where components mounted on your panel. is the most crucial facet of PCB production. During assembly, the components guaranteed with a soldering method. such as influx or laserjet. To make sure successful soldering, regions of the plank that want solder. like element pads and vias, must isolated from the areas that do not. This isolation achieved with solder masking. The solder mask protects the table from corrosion and oxidation, and without it. the probability of premature PCB failing is higher.
 
  In a few situations. it’s hard or advisable to use solder masking; for example. where in fact the splitting up between pads is small, where warmth sinks used. so when the pitch from an element is very fine or too near to drill openings. Areas where solder mask shouldn't applied described by solder mask clearance limitations, . which described by your agreement manufacturer (CM). The principal reason behind solder mask clearance limitations is to provide enough spacing. or solder dams between surface elements that receive solder. to avoid the forming of solder bridges. Solder bridges form when solder links. conductive components of the panel which were not designed to linked. Solder bridges can lead to brief circuits or burnt components.
 
  Solder mask clearance defined as an over-all splitting up recommendation. along with particular specs described. based on the kind of surface component(s) isolated. Particular specs connect with pads, which might be solder mask described. or non-solder mask described, and drill openings. which might plated through opening or non-plated through gap. 
 
SolderMaskClearance, PCB

 

 
 

 Solder Mask Expansion

 
  Most PCB design software programs. allow you to create the distance between your solder mask. and surface elements (for the whole plank). or (for elements). It could also be possible to create both these design guidelines. and allow this program to apply guidelines to look for the specification to use to each case. This parameter is also known as the solder mask growth. and may maintain positivity, zero or negative.
 
  Positive solder mask development means. there is a distance between your pad external perimeter. and the finish of the solder mask around it that uncovered.
 
  no solder mask enlargement entails no space. or “space” between where in fact the pad ends and the solder mask begins.
 
  Negative solder mask growth is present when the solder mask covers some of the pad. The worthiness is the length. between your pad perimeter inward to where in fact the solder mask halts.
 
  Generally, it might be ideal to have zero solder mask development. which provides the mandatory solder dam. and maximum table safety. But, there are instances where it might be easier to have negative enlargement, like. when applying via tenting, that involves covering a. via to avoid solder from attracted into the opening. it is advisable to specify the positive or negative solder mask growth. that is manufacturable predicated on your design needs. and aligns with your CM’s equipment features.
 
 

   Choosing the proper Solder Mask Clearance for Your PCB

 
  Much like other tolerances for your PCB design. your solder mask clearance should customized to your CM’s specs. As we've seen, solder mask clearance is important to PCB assembly and. if insufficient, can lead to brief circuits. or even element damage. Another important parameter that needs to. used as essential to facilitate the PCB assembly process is solder mask development.  which defines the splitting up between your solder mask and surface elements. To be able to choose the best solder mask clearance for your PCB.  you should seek advice from your CM to make sure that your specs fall of their equipment features. and requirements. Additionally it is smart to consider the next: 

SolderMaskClearance, PCB
 

Soler mask application

 
     The most basic solder mask option is to use a silkscreen to print a liquid epoxy over the PCB. This is like airbrushing face paint on with a stencil. This involves using a woven mesh to support ink-blocking patterns.
 
     Fancier solder masks use a photolithography. process with either a dry film or a liquid solder mask. like that used for photoresist exposure in semiconductor fabrication. LPSM can silkscreened like an epoxy, or it can sprayed over the surface. which is often a cheaper application method.
 
     In this process, a photolithography mask. that matches your desired solder mask made from your Gerber files. Your panelized board is then cleaned to ensure no dust particles trapped. under the hardened solder mask. The panels are completely covered on both sides with the liquid LPSM.
 
      One thing you will notice with LPSM is. that the black portions of the photolithography mask define areas. where you want conductors to exposed, while areas of the board. that you want covered in solder mask will be clear.
 
     Solder masks re applied as an epoxy or a photoimageable polymer.
 
     Once the boards covered with LPSM, the boards dried in an oven and placed into a UV developer. The photolithography mask aligned over the dried board. and the board illuminated with UV light. The exposed areas of LPSM material cured by the UV light. while the unexposed areas washed off with a solvent, leaving behind a hard layer of solder mask.
 
     DFSM applied in a similar process as LPSM. Both exposed in a photolithography-type process. and the unexposed areas removed with a solvent. The difference with DFSM is that the unexposed solder mask material. must be vacuum laminated onto the board to avoid creating defects with air bubbles.
 
     No matter which type of solder mask material you use. the resulting solder mask will leave exposed areas of copper on the board. These exposed areas must plated with a surface finish to prevent oxidation. The most common surface finish is hot air solder leveling (HASL). although other popular surface finishes are electroless nickel immersion gold (ENIG). and electroless nickel electroless palladium Immersion gold (ENEPIG).
 
     The thickness of your solder mask depends on how thick the copper traces on your board. LPSM and DPSM solder mask thickness in empty areas of the board. will generally vary with location. The typical solder mask thickness (perpendicular to the board) is at least 0.8 mils. Solder mask will be thinner near the edges of traces and can reach as thin as 0.3 mils or less. In general, you’ll want about 0.5 mils of solder mask over your traces. Sprayed epoxy solder mask can take a more uniform thickness. throughout your Printed Circuit Board.
  
      The lateral thickness of solder mask is quite important. when working with fine pitch components. such as high pin count BGAs. In addition to preventing corrosion on copper traces. solder mask used to place a dam between neighboring pads on a component.
 
    The color of your solder mask determined by the dye used in the solder mask material. and the chemical properties of the dye. will influence the cured solder mask thickness. One reason that green solder mask used is that it can used to create thin solder mask dams (~0.1 mm). The dyes used in solder masks with different colors tend to form thicker solder mask dams. No matter which dye you choose to use, solder mask thickness on PCBs for. use in certain industries or applications defined in IPC-SM-840D.
 
     Like any other fabrication parameter or process. you should consider how sensitive your final application will be. and plan your design . It's always important to discuss the fabrication options with your manufacturer. They may even be able to suggest better options based on their capabilities.
 
       Deciding on an appropriate solder mask. depends on the physical dimensions of your board, holes, components. and conductors, the surface layout, and the final application for your product.
 
    First, if you have a Circuit Board solder mask that will used in aerospace, telecom, medical. or other “high reliability” industries, check on industry standards around solder mask. and your intended application in general. There are specific requirements that supersede whatever else you learn on the internet.
 
    For most modern printed board designs, you’ll want a photoimageable solder resist. The surface topography will dictate whether to use a liquid or dry application. A dry application lays down a uniform soldermask thickness across the entire surface. But, dry mask adheres best if your board surface is very flat. If you have complex surface features. then you’re better off with a liquid (LPISM) option for better. contact with the copper of your traces and the laminate. The downside to a liquid application is that the thickness isn’t uniform across the board.
 
   You can also get different finishes on the mask layer. Talk to your manufacturer about what they have available. and how it will affect production. For example, a matte finish reduces solder balls if you are using a solder reflow process.
 
    PCBs manufactured using a solder reflow process need a solder mask. The finish of the mask can affect the quality of the reflow.
 
    When you design your printed circuit boar, the solder mask should be its own layer in the Gerber files. Check the design rules for a solder mask layer. Usually, you'll want a 2 mil border around your feature in case the solder mask isn't centered. You'll also have a minimum distance between pads, often 8 mils. to ensure the mask is enough to prevent solder bridges from forming.

     Printed circuit board solder mask options from Millennium Circuits Limited. designed to meet your industry needs. We focus on the technical nature of your PCB. such as elements like controlled impedance . and allow your team to make the PCB mask choice based on what you feel is most pleasing for your application.

PCB Solder Mask colors 
 

Green Solder Mask 

      The green standard is still a common PCB solder mask option because it allows everything to seen . White text on the green background has a high amount of contrast. and the finish isn’t bright enough to reflect too much light, so there’s a reduction in glare. Green is a common choice for boards that must inspected. plus some may find. it to be an effective method to highlighting high-quality craftsmanship. because the color does not get in the way of showing off the routing.
 

White Solder Mask

     White printed circuit board solder mask applications are. becoming more common. because they can make a PCB look especially pretty in a clean environment. They make stunning show models in many situations. but, real-world applications can be more difficult . because the white solder mask hides traces very well. Inspection can become nigh impossible in some situations. especially if you’re in a room with only direct overhead light. One area where it does shine, but, is in the use of black silkscreens because of their stark contrast with white.
 

Black Solder Mask

     Black solder masks produce less of a visibility concern compared to white options. Contrast is minimal but labeling and large components are easy to see. The downside is that light may catch the component and cast a small shadow. making traces that much more difficult to see. Black PCB solder mask options are also not recommended because of the increase in heat. which may discolor silkscreen and make the board more difficult to clean. Like white, it’s a very pretty board to observe. and can create a distinct visual if you’re trying to highlight a capability of yours.
 

Red Solder Mask

      Red boards are becoming a popular option. because they provide good visibility and contrast for planes, traces. and even your empty space. It’s less contrast than green boards but will give a PCB a feeling of freshness when compared to stale. industry standards. Silkscreens stand out well against the red.
 

Blue Solder Mask

     Label-heavy boards should consider a blue liquid photoimagible solder mask. because of the significant contrast it creates with silkscreen. Traces can become much more difficult to see without proper lighting and magnification. so that’s the balance point for this blue option. Blue is often chosen for how it can look. It isn’t as striking as white or black. but it does provide a compelling aesthetic choice that implies complexity and craftsmanship. especially if you’re mounting it against an LCD. It is a little more likely to show dirt compared to some other colors.
 

Yellow Solder Mask 

     Many new colors are emerging, but they can be difficult to manage. Yellow is a pleasing color. but it contrasts with both silkscreens and traces. making it difficult to use in any real-world application. Different colors will balance different needs, such as cleanliness, visibility and style. Always try a sample before running with your new color choice.
 
     In the past. it’s important to note that these options were available to most PCB manufacturers. but customers rarely indicated a preference. so the final decision ws left up to that manufacturer. You should always consider the benefits of each option when making your decision.
 
      The good news is that your board will not perform with a matte or gloss finish. From a pure solder mask standard setting, each will leave your board in the same place. That means aesthetics and some limited field use should guide your decision-making process.
 
      A matte finish is duller, softer finish. This means it will not reflect a lot of light but can look washed out under a heavy light. You’ll also see more scratches with a matte finish. they appear darker and don’t have a true shine, making them easier to look at in more lighting scenarios. Matte finishes may make it easier for you to detect problems with a PCB.
 
     The gloss finish option is a harder but lighter color that tends to reflect a little more light in the total. but, the details in the PCB are not lost as often in harsher light as they are in a matte finish. This means gloss solder masks show less wear, such as scratches. A gloss finish that is more reflective may make inspection more difficult.
 
      This is an aesthetic choice because matte. and gloss finishes tend to cost roughly the same and applied. through the same process during manufacturing.

how to solder a circuit board

 
      Soldering is the process of using a filler material (solder) to join pieces of metal together. Soldering occurs at  low temperatures (around 400 degrees Fahrenheit) as compared to brazing. and welding, which actually melt and fuse the materials themselves at higher temperatures. In soldering the filler material becomes liquid. coats the pieces it  brought into contact with and is then allowed to cool. As the solder cools it hardens, and the two materials  joined. Soldering is a quick way to join many types of materials, from copper pipe to stained glass. It creates an electrically conductive strong bond between components. that can be re-heated (desoldered). if you should ever want to disconnect two items joined together. It's great for joining electrical components and wires. and  used in  about everything electronic. In this Instructable I explain how to solder the basics. you see in most Instructables: electrical components and wires.
 
      Soldering a circuit board requires special kind of considerations. you can start by placing a wire in its holes, put your solder iron tip near to the holes. and wire for a second and then apply solder. Remove your solder iron, wire and carefully inspect whether the solder joint is okay or not.
 
      Soldering on a PCB Put the tip of the iron on the pad so that it heats both the lead of the part and the pad of the circuit board. Heat them for a second or so before you apply solder. Remove the iron and the solder wire and inspect your solder joint to see if it looks okay.
 
      As with many skills, having the right tools for the job effects the quality of the work  done. When it comes to soldering you can end up using a lot of fancy tools. or  a few simple items you can pick up at the hardware store for a couple of bucks. I am going to use a couple of different soldering tools in this Instructable. there are many ways to solder, and you should use what works for you.
 
       At the very minimum you will need the solder and a heat source to melt it. something small which can get to 600-800 degrees Fahrenheit. If you've got that, your ready to make a connection. That  said. there are a wide range of soldering tools and accessories that can be really helpful. if you're going to be soldering frequently. Ladyada has compiled a nice list of equipment and sources to buy the tools on her site. I got together a solid supply of soldering tools by raiding the Squid Labs soldering station. 
 

 
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