- PCB stencil services at cost-effective prices
- No minimum order requirement, SMT stencils order start from 1 pcs
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- Frame stencils and Frameless stencils
Your Valuable PCB Stencil Supplier
In order to meet Surface Mount Technology(SMT) requirements, assembly factory will need to source PCB stencil (also called SMT stencil, SMD stencil, solder stencil or solder paste stencils) for all PCB assembly projects, unless your PCB assembly is 100% DIP( through-hole) components.
PCB Stencils (SMT stencils) play an important role in transferring accurate amount of solder paste to correct positions on bare PCBs which are ready for assembly. PCB stencils enable you to use metal squeegee blades to apply solder paste easily over the openings on PCBs and make a stencil to be well aligned with the surface of the bare PCB.
Your Leading PCB Stencil Supplier in China
Venture provides two types of PCB stencils: laser-cut stencils(laser stencils) and chemical-etch stencils according to customer requirement.
- Laser-cut PCB stencils(laser stencils) are made of 100% stainless steel foil with high accuracy by laser, perfectly suited for fine pitch and BGA assembly, 90% of our PCB assembly use Laser-cut stencils. Our laser PCB stencils provide optimum solder paste volume control, and have smooth aperture walls and can be used for 16 Mil pitch and below and for Micro BGAs.
- Chemical-etch PCB stencil means the openings on the stencils are etched( not lasered) into the metal using acid. Usually, this kind of PCB stencil offers better protection on material temper and hardness, but tending to form sand clock shape or large openings and unsuitable for fine pitch and BGA assembly.
You are welcomed to add a PCB stencil(SMT stencil) to any of the PCB fabrication orders or PCB Assembly orders. Simply place your PCB order with our sales as usual, and choose from proper stencil types and sizes that fit your PCB stencil requirements.
Venture offers Framed PCB (SMT) stencils and Frameless PCB (SMT) stencils
- Framed PCB Stencils (also called glue-in stencils) are laser cut stencil foils permanently mounted in a stencil frame using a mesh border to tightly stretch the stencil foil taut in the frame. These PCB stencils (solder paste stencils, SMT stencils) are designed for high volume screen printing on PCBs. They are recommended for printed circuit board assembly with volume production runs.
- Frameless PCB Stencils are also laser cut stencils, these solder paste stencils do not need to be permanently glued in a frame, they are recommended for prototype printed circuit board assembly or small pilot runs, the price for frameless Stencils are much cheaper than framed Stencils.
If you are looking for a high-quality PCB stencil? You’ve come to the right place. Venture engineering team works closely with customers to make your assembly work easy and fast.
No matter you are an electrical engineer, a product designer, a system integrator or a maker looking for stencil maker, Venture will be your perfect SMT stencil maker in China.
Through our 2 hours rapid response services from our 24/7 sales and tech support team, and excellent after-sales service, we will be your best PCB stencil maker in China, pls feel free to contact us anytime for your PCB stencil(SMT stencil) requirement.
PCB Stencil: The Ultimate Guide
PCB stencil is a template that covers printed circuit board with opening where you’ll apply a solder paste.
With the help of a squeeze, the solder paste can be applied very fast through an automated process.
In this guide, we will focus on the definition of PCB Stencil and its importance.
We will also look at techniques for making a PCB Stencil, types, design and use.
Lastly, we will learn about cleaning a PCB Stencil among other topics.
What is PCB Stencil?
PCB stencil is a thin bare stainless steel metal sheet designed with a pattern that allows components to be mounted.
PCB stencil is used for depositing solder paste on a printed circuit board to form electric connectivity.
A stencil can either be framed or unframed. Once stencil has been deposited on to the board, PCB components can be mounted on to the circuit board.
The PCB stencil is made from solder metal and flux.
Importance of Stencil for PCB Assembly
With a well-printed stencil, there is a high likelihood that high-quality PCB Assembly process will be achieved.
For this reason, PCB engineers focus mainly on producing good surface mount technology stencil for printing processes.
This is because the stencil cannot be manipulated to yield the desired results.
A good design for a PCB Stencil helps to reduce PCB Assembly defaults of surface mount technology by between 60% and 70%.
This means that if you want to have high-quality PCB, a good PCB stencil design is very critical.
Stencil makes the PCB adhesive especially during component mounting and soldering. This results in strong solder joints.
It ensures that there is a good formation of sizes and shapes of deposits on to the circuit board.
Techniques for Making Stencils
During our discussion about these techniques, we will also see the materials used in each of them and their individual capabilities.
Lastly, we will look at the advantages of each technique.
You can make your own image or download one and stencil it.
Materials used in this technique are vector art files, a very sharp knife, colors, and metal plate-like aluminum.
Here, the technique involved is vector cutting.
Beams of a laser cutter follow either one or more paths defined by the vector cutter.
The laser beams are directed at the material that being used to make the stencil.
Cut areas are molten and evaporated. You can also burn or blown them away using an air compressor, leaving an edge of Stencil with a good surface finish.
Laser-Cutting technique for making stencil promotes smooth aperture wall. This promotes paste release in a more efficient way.
This is a technique of stencil making that is done using an electroplating method. It is made from Nickel alloy.
Besides, it is capable of producing a smooth aperture wall which aids in easy paste release.
It produces flat and smooth aperture inside the wall of the board. This is ideal for fine pitches which can be used in Surface mount technology.
Also, the paste can be released easily and efficiently. This technique allows for a stencil to be made with varied thicknesses as may be desired.
This is a technique that involves subtraction of some parts of copper from a printed circuit board.
Acid is used to remove unwanted copper from a prefabricated board. Desired parts are covered using a temporary mask.
Chemical etching PCB
Etching of a PCB can either be done at home or in a laboratory through a simple and cheap process.
There are two types of acids that can be used: Ferric chloride and sodium persulfate.
Here, you’ll require a spraying machine that should also control the temperature.
This technique requires that a spraying machine being used to spray the chemical is expected to control the temperature.
It also keeps the fluid in motion during reflow on the prefabricated board.
Etching is capable of producing either single or small circuit boards particularly when you want to reduce production cost.
The use of the sprayer decreases the etching time.
Normally the quantity of acid being used is also reduced when a sprayer is used. This also contributes to the reduction in stencil production cost.
Its stencils have better open areas thus improving paste transfer on to the PCB pads.
It can work well for Surface Mount Technology with fine lead pitches even as low as 0.8 mm.
This is very important because SMT PCBs can be used to make small devices which have small apertures.
This technique of making stencil uses files that contain daffodil blossom from a hybrid kit.
The hybrid kit is placed on a blank document of about 8.5 x 11 inches.
Here, you can crop out a single daffodil image of a flower.
Next is to add black dots on either side of the blossom and crop the image. Once the image has been cropped out, select and duplicate them.
Collectively, select and drag all the duplicated images to an open space on the blank document.
Make sure the first and second sets of the images are identical, that is, there should be no image adjustment.
Print out the images onto a print paper. This print out will maintain the stencil even after several ink applications has been made.
How to cut hybrid stencil
On a cutting mat, a daffodil is trimmed around a perimeter of the paper.
The second image which was duplicated is also trimmed at the center using a craft knife.
With the help of a punch, black dots are punched at a size of 1/8 inches on a marked paper.
How to work with the stencil
This stencil is laid on a paper and ink is carefully pulled from the edge of the stencil.
Ink is pulled into the trimmed areas that now appear open. Using a pencil, light marks are made in the punch holes.
The stencil can then be slide to align with the second punched holes. After this, ink is applied to the daffodil center that was trimmed.
Once it is done, the stencil is removed and pencil marks are thereafter erased.
This same procedure can be repeated for as many hybrid stencils as you desire to make.
Through this technique, you can be capable of producing many different hybrid stencils.
This technique is simple and clear to use. It is also relatively cheap as compared to other techniques for making stencils.
It can be used to make different PCB Stencils so long as you have different hybrid kits.
Also, it does not require costly machines like other PCB Stencil making techniques.
The risk involved during stencil making is very minimal, unlike chemical etching technique.
It can consume a lot of time since it is done manually.
Because its production consumes time, making many hybrid stencils is not easy.
PCB Stencil Types
There are two main PCB SMT Stencil types:
- Framed SMT stencils
- Frameless SMT stencils.
Let us now look more intensively at these two
1.Framed SMT Stencils
Also called ‘’ glue-in stencils, these are the strongest laser-cut stencils that exist in the current market.
They are designed mainly for high volume screen printing of PCBs.
Framed PCB Stencil
Solder paste is mounted in a stencil permanently using a mesh which tightens the stencil on the frame.
They are excelling in the market today because they aid a unique process of aperture walls that are smooth.
Also, they produce very clean laser-cut apertures which are good for high volume stencil printing.
They are used for micro BGAs and also to produce permanent and non-fading fiducials.
2.Frameless SMT Stencils
These are also known as foils. This stencil, unlike a framed one, is not glued permanently in a frame.
A frameless stencil is usually preferred for short runs or prototype PCBs.
Frameless PCB Stencil
This stencil is made using stainless steel with laser cutting technology.
It has a thickness of about 0.002 – 0.016 inches with a minimum width cut of 0.002 inches.
Its aperture tolerance is 0.00025 inches and it allows for fiducial and panelized data.
This type of PCB SMT stencil is less costly as compared to framed one. However, it still produces high quality and good performance devices.
Space required for storage of stencil is reduced since it does not have a frame.
In addition to these, its smooth aperture walls can be used for Micro BGAs of16 mil pitch and below.
PCB Stencil Design and Use
A PCB Stencil helps to accurately deposit the correct quantity of solder paste onto the surface mount pads.
When this is done accurately, it promotes good solder joints between the PCB pad and component terminals.
These joints therefore promote efficient electrical connection and mechanical strength.
SMT PCB Stencil
i. Design Considerations
It is important to put some factors into consideration when we want to design and use PCB Stencil.
These include stencil:
- Aperture design
Let us look at these design considerations one by one giving more insight into each of them.
Good paste deposit onto a PCB is dependent on the relationship between pad size, aperture opening, and thickness of the foil.
Stencil thickness ensures good paste release from the apertures.
Thicker stencil than the size of an aperture results in surface tension holding paste to the inner aperture walls.
For example, laser-cut stencil which has a component of 16 mils (aperture width of 8 mils) should have a thickness of 6 mils* (6 x1.2 = 8).
Aperture design helps to stop solder defects like bridging and solder beads from forming.
The design depends on whether the pitch of the aperture is fine or not.
When it is fine, it has to be slightly smaller in comparison to the pad size that should be landed.
This aids a good gasket seal between PCB and Stencil.
Also, it helps in improving the strength of the joints between the landing pad and the underside of the stencil.
Some apertures need to be designed in a special way to allow less paste to be deposited on the inner edges of the pad.
It helps in reducing the possibility of mid-chip solder balls from forming.
For instance, the diagram below shows a home plate aperture which is a solution to mid-chip solder balls.
The adjacent illustrates a mid-chip solder ball.
The table below is an illustration of standardized aperture and pad sizes.
|Pitch component||Standardized Pad width||Standardized aperture width|
|The component pitch of 50 mil||Pad with of 25 mil||Aperture width of 25 mil|
|The component pitch of 40 mil||Pad with of 20 mil||Aperture width of 20 mil|
|The component pitch of 31 mil||Pad with of 17 mil||Aperture width of 16 mil|
|The component pitch of 25 mil||Pad with of 15 mil||Aperture width of 12 mil|
|The component pitch of 20 mil||Pad with of 12 mil||Aperture width of 10 mil|
|The component pitch of 16 mil||Pad with of 10 mil||Aperture width of 8 mil|
|The component pitch of 12 mil||Pad with of 8 mil||Aperture width of 6 mil|
During the design of aperture, if its reduction is needed, it should be done from all sides. This is important because it has to remain centered on the pad.
iv.Stencil material and mounting
The type of stencil material determines the ability of the paste to pass through the aperture.
Stencil materials can be a specified thickness of a flexible flat smooth surface of Kapton material or Mylar.
It can also be a thin surface of stainless steel with inner cutout edges that are smooth.
This helps in releasing of the solder paste. It can be as thick as 16 mils and to allow placing of more solder paste onto the pad.
In addition to these, some stencil is made using nickel. These types of PCB stencils can be laser-cut, or chemically etched out.
It is more expensive as compared to a stainless steel one.
Alternatively, the coating can be applied to these materials from time to time to improve the release of solder paste through the aperture.
For example, NanoProtek coating can be used although it requires a periodic application and this is also an additional cost.
v. PCB Stencil material mounting
This is the transferring of solder paste on to a bare board. It creates space for all surface mount components onto a board.
PCB Stencil mounting can either be done permanently to a framed bear board or temporarily in the frameless board.
Framed stencils are used for high volume PCB printings which are expensive.
On the other hand, frameless ones are used for low volume PCB printings which are cheap and easier to store.
Fine pitch devices should use thin stencil whereas larger parts require thicker stencil.
Therefore, mounting of the components here calls for the step-up and step-down design of a stencil.
Step-up for fine pitches can be created through the addition of some materials to the stencil.
It is done so that the volume and height of the solder paste in some selected areas can be increased.
On the other hand, when a step-down is required, some stencil materials are removed.
This is done to reduce the volume and height of the solder paste deposited in a selected area.
Successful printing is ensured when apertures are designed with a minimum distance from step edges.
The step edge is also called keep out area and mainly depends on step dimensions.
Remember, the picture below shows the standard thickness of stencil and step-down areas as discussed above.
It is very important to have good alignment of the stencil to the PCB.
This is because it aids in the achievement of an accurate deposition of solder paste to the pads.
You can ensure accuracy through the addition of fiducial marks not only to the PCB but also to the PCB Stencil.
For example, the diagram below illustrates fiducial marks as an important factor that has influenced the achievement of good alignment.
vii.PCB design specific
Sometimes, components within the PCB design have large copper pads below the device.
This provides good electrical connections which are used to dissipate heat.
When the whole pad area is applied with solder paste, it results in device lifting. In addition to this, the outer leads will not be soldered.
The solution to this problem is to create a window effect in a stencil aperture design.
Normally, this window effect reduces solder volume as you can see in the figure below.
PCB design can sometimes have vias within a large copper pad to dissipate heat from the device.
This can cause unpleasant results.
When this happens, a special design for a stencil aperture can help to prevent solder paste from being deposited onto the vias.
Look at the figures below:
How to Clean PCB Stencil
Many PCB Assembly industries experience the problem of a dirty stencil.
Cleaning is very simple although it can cause a headache due to the inconsistency of cleaning quality and labor issues.
A PCB stencil can be cleaned using different liquids.
For example, you can either use Isopropyl Alcohol (IPA), which removes solder with minimum efforts.
Methylated spirit can also be used to clean a PCB Stencil. It also works well but not like IPA.
With these liquids, use an old rag to clean off solder paste.
The use of tissue paper and steel wool has some shortcomings and therefore, are not very much preferred.
This is because the tissue bits are left in the holes. Also, the steel wool catches the holes, pulls and ends up damaging the stencil.
Methods of Cleaning APCB Stencil
Cleaning of A PCB stencil can be done through three different methods:
- Manual soak PCB Stencil cleaning
- Pneumatic spray PCB stencil cleaning
- Ultrasonic PCB stencil cleaning
SMT Stencil PCB
a)Manual Soak PCB Stencil Cleaning
The tools and materials required to clean a PCB Stencil manually are cleaning agent, duster cloth, special gloves, sprayer, and a container.
Once you have all these tool and materials, spray cleaning agent on the stencil.
Alternatively, you can soak the stencil into a cleaning agent in a container for some times.
Check if the solder has condensed into pieces on the PCB Stencil.
With the gloves on your hands, swab down the dirty parts containing solder paste using a duster cloth.
Dry the stencil using an air compressor.
After drying, confirm if solder residue has been removed and the PCB Stencil surface is clean.
Also, the mesh should remain without any clogging.
Check also that the mark points have not been damaged during the cleaning and drying process.
Lastly, confirm stencil tension.
This method is preferred because it is relatively cheap compared to other methods. It also has a good visualization.
Manual soak PCB Stencil cleaning takes a considerably longer cleaning and drying time.
Therefore it is relatively less effective.
Cleaning depends on the effort of the cleaner. This means quality variations because individuals differ in ability and precision.
It is prone to damages caused by human error.
b)Pneumatic Spray Cleaning
This is an automated PCB Stencil cleaning method.
A pneumatic stencil cleaning machine, cleaning agent and special gloves are the tools and materials used in this method of cleaning.
Put the Pneumatic stencil cleaning machine on and cleaning and set the drying time.
Put the stencil into the machine and leave it till the designated time when it automatically stops.
You can then remove the stencil and redo the process on another machine to perfect the results.
All these processes are automated except loading and offloading of the stencil into the machine.
It is highly effective and relatively easier to use than the manual option.
Remember, it is also automated without power.
That is, the pneumatic stencil cleaning machine works automatically without having to be connected to any power source.
This method is very economical in terms of manpower.
The machine does both the cleaning and drying. Therefore, many PCB stencils can be cleaned through this method just by one machine operator.
Cleaning of larger sized PCB Stencils is almost impossible using this method since they can’t fit into the machine.
Also, its cleaning effect is not good for thick PCB stencils.
It is relatively expensive as compared to the manual method since the machine used has to be budgeted for.
c)Ultrasonic PCB Stencil Cleaning
This method uses an ultrasonic stencil cleaner machine, and a cleaning agent.
Put the machine on and set up cleaning and dying time, which automatically stops on completion of the task.
The stencil is removed once it is clean and another put into the machine to continue with the cleaning process.
This method of PCB Stencil cleaning is fast since it is automated.
It is also very highly effective and the PCB Stencils cleaned through this method yield very clean stencils.
It cannot be used to clean large or oversized stencils because they cannot fit into the machine.
Also, the method is more costly than the manual one due to the cost of buying the Ultrasonic cleaner machine.
Procedure in Using PCB Stencil
The procedure for using PCB Stencil is very simple. You will need:
- L-Shaped boards-both large and small
- Flat surface fixture
- Solder paste
- PCB components
With the above materials, the following is a step by step illustration on the procedure.
- Place a large L-shaped board and tape it on a flat surface fixture to prevent both the stencil and the board from moving about.
- Take your PCB stencil and place it into the L-Shaped fixture. This L-Shaped fixture has ninety degrees corner where the PCB stencil fits very well.
- Place the small L-Shaped board fixture in the opposite corner that is not covered by the larger L-Shaped fixture. This is also done to prevent movement and it is also taped down.
- Align the stencil over Surface Mount Technology pads where they are taped down at the L-Shaped brackets flat edge.
- Apply solder paste on one edge of the prototype stencil.
- After applying the paste, make a single pass over the apertures to deposit the solder paste using a squeegee.
- Go ahead and remove the board from the fixture.
- The board now is ready to be mounted with components. Therefore, using pick-and-place vacuum tool, place the components in the paste.
- The last stage is to place Temperature markers on the board. This can be done using either toaster oven, hot plate or heat gun to heat the board for reflow.
When the board is heated, the changing color will be indicated by temperature markers.
Performance Issues with Solder Paste and Stencils
Solder paste flow is very crucial when we want to define a PCB stencil performance.
This primarily depends on the materials and physical structure of a PCB stencil the paste is expected to pass through.
Solder paste and stencil can sometimes have issues, which can compromise the quality of solder joints that are formed after reflow.
This can lead to faults in the PCB Assembly process.
Solder paste stencils
Let us therefore go through various solder paste and stencil performance issues and some possible resolutions to the same.
·Poor solder paste wetting.
This can be caused by different reasons.
For example, when the surface being soldered has been oxidized, or when solder paste volume is very low.
It also happens when a soldering temperature is uneven.
If you want to know that you have a good solder paste, there will be no gaps or areas missed.
When this is the case, 100% solder paste is achieved.
This is what we call high wetting value.
It aids a better spread of solder paste when carrying out reflow, resulting in strong and well-developed solder joints.
Solder paste and stencil performance issues can be tackled through an evaluation of solder paste.
This can be done within minimum time possible.
The evaluation uses quantitative data generated from samples of solder pastes to be tested.
Remember, the baseline can be the current solder paste which is used for comparison to other solder pastes selected.
The method for evaluation should be challenging enough to show both the advantages and disadvantages of the selected solder pastes.
You can use high activity solder paste: For difficult to wet surfaces like immersion silver, immersion tin, and OSP, wetting difficulty increases after the first reflow.
Consequently, high activity solder paste should be used. Oxidized surfaces can also use this wetting prevention method.
Minimize oxidation on the surface where solder paste is supposed to be applied: Working with less oxidized materials is next to impossible.
Therefore, you can use nitrogen during the reflow process. This nitrogen will help to minimize oxides that pile up during the reflow process.
Use more solder paste, or alternatively, use larger leads:
The larger leads compensate for the low volume of solder paste and eventually leads to the completion of good solder joints.
You can also adjust reflow profile: This will promote good wetting of both the pads and the component leads.
Increase soaking time so that solder temperature can be equalized and trouble spots eliminated.
Soaking a PCB stencil for longer period aids complete reflow of the liquid solder before it can start freezing.
Clogging and incomplete transfer of solder paste onto the PCB pads
This happens when the stencil aperture is too small to allow adequate solder paste to pass through the PCB pads.
Solder paste stencil
This can be prevented by using flip-chip to apply solder paste on to the PCB.
This is a solder paste performance issue that happens when two solder joints melt together.
It then forms an unintended solder joint. This happens when excess solder paste is applied on to the stencil pad
To avoid this issue, you can change the design of the stencil. The design is changed through adjustment of aperture width and area ratio.
Also, solder mask dams can be added in between fine pitch pads to prevent solder paste bridging.
When the stencil is subjected to movement when the solder paste is solidifying, the result is disturbed joints. These joint appear rough in texture.
Sometimes, it can be seen as cold joint, but it is not.
This is because they just look alike but what causes it differs from the cause of a typical cold joint.
A disturbed joint can be repaired when reheating is done and then allowed to cool undisturbed.
Prevention of disturbed joint
To prevent this, you have to make adequate preparation by immobilizing the joints.
You can also use some vise to stabilize your work during reflow.
Too much Solder Paste
You may think that this produces a perfect joint but this may not be the case.
It does not provide a reliable electrical connection. A surface that gives good electrical connection has a nice concave surface.
Too much solder paste can be repaired by using solder paste sacker to remove excess paste from the joints.
When some solder pastes deposit reflow before the others, lifting of components occur.
This is common with small components attached to circuit boards that are attached to one end of a ground plane.
This results in temperature difference from one end to the other.
Prevention of Tombstoning
Make an anti-tombstoning solder paste using a mixture of an alloy which creates a melting range.
PCB Stencil DIY
You can make a PCB stencil from home using some computer programmes and readily available materials.
The DIY (Do it yourself) method is preferred because it is cheap and quick.
One method that you can use to make PCB stencil by DIY is by using Silhouette portrait.
To do this, you will need the following materials:
- Silhouette portrait machine
- A backing sheet of silhouette which has one sticky side
- Material for making a stencil, for example, Vellum
- Solder Paste
- SVG file from a PCB for stencil
Procedure for making PCB Stencil DIY
Export an SVG file for paste layers of your PCB.
From Ki Cad in Inkscape, open SVG, resize it to 125% since it appears smaller than the actual board pads.
Save it as PNG because this is what silhouette studio basic program uses.
Measure the length and width of the board. Using these measurements, expand the size of the graphic until it is around 0.5 inches x 0.5 inches.
This will enable you to come up with a reliable Stencil.
You can now create the boxes that you would like to cut using box features in silhouette studio.
To cut from vellum, highlight silhouette and ensure it coincides with the copper pads where solder paste will be applied.
The next step is to prepare the vellum and the silhouette for cutting.
Attach vellum on the sticky part of the grid plastic sheet at the center between the rollers on the silhouette portrait.
Press the top button.
This feeds the plastic sheet to its starting spot automatically. Make sure you don’t use the second button or else you can end up cutting the plastic sheet instead.
Using the silhouette studio program, use the right icon to send it to the silhouette.
You can now press the start button and watch how silhouette cutter does its job.
Upon completion of cutting, silhouette releases the rollers towards you.
Press the middle button and complete unloading of the grid plastic sheet.
Peel off the vellum and using a brush removes any straggling squares that might be hanging on the vellum.
You can take the vellum and compare it to the board so that you can determine whether you can use it or not. If they are similar, then it can be used.
Test it by applying solder paste from one side and squeegee it towards the other side.
Go ahead and use it as an actual stencil.
Advantage and Disadvantage of PCB Stencil DIY
It is simpler and cheaper way to make stencils.
It is the best way to go if you need your stencil fast, because it generally takes a shorter time to make stencils by DIY.
However, this option has a weakness because the process does not include stencil cleaning, meaning the stencil so obtained will may have some problems.
PCB Stencil is very crucial in the industry of PCB Assembly. This is because a good stencil is the beginning of good quality PCB SMT devices.
Once the stencil has been made the right way, other components are mounted onto the PCB into the right positions.
Therefore, all PCB Assembly engineers have their main focus on making good quality stencils which are relevant for specific devices.
The end product of their devices is eventually good and marketable.