Why Step Stencils are indispensable in your PCB assembly

Miniaturization of electronic devices and components is a real trend. Designers are constantly working on the edge of the physical limits of manufacturability. As a result of this the apertures in stencils are always getting smaller. Who still remembers the times that a chip component of 2 by 3mm was really small? Nowadays components of 0,2 by 0,4mm are no exception!

As soon as the design is made and the PCB’s and components are purchased, assembling all the parts on a production line is the next mayor step. In this step stencils play a very important role.

PCB components are getting smaller and smaller.

Miniaturisation of PCB components over the years.

Traditional stencils vs. Step Stencils

The common traditional stencils have a certain thickness along their entire surface. Because of miniaturization an increasing need for stencils with areas of lesser or more  thickness has grown.
These type of stencils are called stepped stencils.

The minimum dimensions of the stencil apertures are depending on the stencil thickness. Smaller apertures require thinner stencils. As a result the choice of solder paste has to be reviewed.

Stepped Stencil example

Example of Step Stencil

Step Stencil voorbeeld

The importance of a solder paste

Solder paste is a mixture of fine grain solder powder and a gel flux. A solder paste is continuously subject to evolution. The grain size of the solder paste determines the filling of the apertures. The thinner a stencil, the better the release of paste from the stencil and the better the transfer of paste to the PCB will be.

Two decennia ago the standard powder in solder paste had a grain between 25 – 45 µm, nowadays the grain size has dropped to 15 -25µm.

The current solder paste machines have to be able to print complex electronic boards with a repeatable accuracy and very high precision. A robust, stable and high technological machine design is crucial in this process.

To excel in PCB assembly with the ESE stencil printer

The US-X series of stencil printers of the renown South Korean brand ESE has it all to fulfil and even surpass the highest production requirements.

The hart of the machine is their unique and robust printing table which has 4 ball screws along with 3LM guides. This design is unique and crucial and enables stable print accuracy of within 10µm and these are combined with a 12,5µm repeatability.

Print table ESE stencil printer

ESE’s robust, accurate and unique design print table

ESE’s US-X series is a very comprehensive machine with some very interesting features:

  • Very intuitive software interface
  • 2D inspection
  • Under stencil cleaner,
  • Automatic support pin placer,
  • Solder paste high check,
  • SPI feedback,
  • Seamless board clamping,
  • Internal climatisation
  • Fast camera

Feedback of SPI data

An Solder Paste Inspection system (SPI) is an essential part of an SMD assembly line. An SPI system measures the shape, volume, the coverage and the positioning of the printed solder paste on the PCB. When these measurements are out of tolerance the SPI will report this and will send this data to the ESE printer.

The SPI can report clogged apertures to the ESE printer which will activate an additional cleaning cycle of the under stencil cleaner. Also the alignment in the printer can be corrected.

A leading manufacturer of automatic optical inspection systems for the electronic industry is the SAKI corporation. Their 3D solder paste inspection system inspects the whole surface of a PCB very accurately and fast.

ESE Stencil Printing US-X-series

ESE Stencil Printer US-X-Series

SAKI 3D Solder Paste Inspection (SPI)

The combination of the ESE printer and SAKI SPI ensures very reliable production of semi conductors and electronic PCB’s

Would you like more info?

Feel free to get in touch!

Bart van de Lisdonk
Service & Process Expert
0032 14 47 19 83

Whitepaper | SMD Production – NOT made in China

More purchasing and production closer to home give us more security and make us independent of a few superpowers. But what about the cost Preview whitepaper reshoring price? Aren’t they much higher given the high labour costs in Western Europe?

To be able to compete in this reshoring, we need to “use the necessary hands as optimally as possible”, but how do we go about this?

In this whitepaper you can find:

  • A roadmap to optimise your SMD production process
  • The answer to the question if a complete SMD production line should be of the same brand

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Whitepaper | Save energy in your production process with vapor phase

In times when energy is very precious and we have to take care of nature, it pays to take a closer look at your existing soldering processes for Preview whitepaper save energy with vapor phase SMD / SMT components. The vapour phase process offers a perfect alternative with the advantage of requiring up to 75% less electrical power.

In this whitepaper we discuss:

  • The vapor phase towards conventional convection system
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  • Saving energy with LMPA

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Whitepaper | Growing in times of electrical components scarcity

The global supply chain of electronic components has been under enormous pressure for some time now. Preview_componentenschaarste_EN

Components are hard to get and prices are skyrocketing. Experts say that we should not delude ourselves too much that this issue will resolve itself in the near future. This is because the need for a microchip, for example, is constantly increasing. The world is becoming more and more digital, which means that more intelligent electronics will be needed.

In this whitepaper, we will discuss in detail:

  • The importance of real-time stock management
  • Plan of action
  • Using fewer components in your assembly

Download now for free!

Become a process expert in Stencilprinting!

In this webinar we will discuss the topic Stencilprinting:

→ How to avoid mistakes in an SMD assembly process
→ What are the most important parameters and conditions
→ What does scooping, slump, printgap and release have to do with stencilprinting
→ Interflux discusses the types of solder paste, the pre-mixing and handling process

This webinar is only in Dutch, please contact us if you want more information in your language.

Become a process expert in Selective Soldering!

In this webinar we will discuss the topic Selective Soldering:

→ How to make a good solder joint
→ What influence do soldering speed, soldering height, choice of nozzle, flux and alloy have
→ Interflux discusses with you the types of fluxes and the need for adapted fluxes

This webinar is only in Dutch, please contact us if you want more information in your language.

Become a process expert in BGA Rework!

In this webinar we will discuss the topic BGA Rework:

→ How to desolder a defective BGA from a printed circuit board
→ How to clean and prepare the PCB to insert a new BGA
→ How to apply flux or paste
→ Which fluxes can be used, what are their characteristics, advantages and disadvantages
→ Which temperature profiles can be used and what do you need to consider
→ Interflux looks together with you at the types of fluxes, pastes, dip pastes, etc.

This webinar is only in Dutch, please contact us if you want more information in your language.

Pin-hole ratio: What is the influence on liquid tin and what ratio is ideal?

Pin-hole ratio

With through hole components, the connection pins go through a PCB. The space between a connecting pin and the hole in the PCB will determine the capillary effect. This effect ensures that the flux and liquid tin are ‘sucked’ up into the space between the pin and the hole.

A good pin to hole ratio is therefore one of the crucial parameters in the successful soldering of through hole components.

Control of the capillary effect

It is important that first the flux capillary is ‘sucked’ up into the hole so that the surfaces of the hole and the pin can be made oxide-free so that the soldering tin in turn can rise optimally.

To get the strongest capillary effect, the open area between the pin and hole must be between 150 µm and 350 µm.

The use of N2 has a positive influence on the capillary action and is particularly important in selective soldering. Also in wave soldering an N2 atmosphere has a favourable effect on the rising of the solder in the holes.

More info?

Leave your details via the contact form and we will contact you as soon as possible!

– Written by Bart van de Lisdonk

What are halogens doing in a flux and what danger do they pose?

Halogens in a flux

Halogens are chemical elements that have the property of reducing metals efficiently. In the process, metal salts are formed that are usually very soluble in water and also attract and retain moisture from the environment. Moisture and metal salts together create an electrically conductive medium. This significantly increases the chance of electromigration and corrosion on electronic circuits.


Electromigration and corrosion often result in electric currents finding other paths to flow than the intended ones. This can have various consequences for the operation of an electronic circuit; malfunctioning, misinterpretation of data, component failure and even the burning out of entire systems.

The metal salt SnCl2 formed by Sn (tin) and Cl (halogen) is almost 100 times more soluble in water than the metal salt PbCl2 formed by lead and chlorine. This means that much more damage can be caused in a lead-free process than in a process containing lead if halogens are used.

How to prevent halogens in a flux

It is therefore necessary to always give preference to absolutely halogen-free soldering products. An IPC Class L0 product still allows a quantity of halogens of < 500 ppm according to the J-STD-004B standard.

Interflux® has a soldering range with ‘absolutely halogen free’ products including soldering wire, solder flux or solder paste.

More info?

Leave your details via the contact form and we will contact you as soon as possible!

– Written by Bart van de Lisdonk

What is voiding and does the reflow profile affect it?


A phenomenon that occurs in the reflow soldering process.

Bubbles (voids) begin to form in the flowed and solidified solder which make the solder joint hollow to a certain extent.

Cause of voiding

The cause of this phenomenon can be found in the outgassing of substances used in the various components, materials and PCBs. However, the main cause of these voids, which are in fact gas bubbles, is the solder paste used.

Solder paste consists of 2 main components, namely metal powder and flux. The flux contains resins and solvents, among other things, which all gas out when heated. When these gas bubbles have not left the liquid tin they become trapped in the solidified mass during the solidification of the solder. Especially in places under components it is extra difficult for the gases to escape because gases tend to move vertically.

How to reduce voiding

To reduce this problem, there are reflow ovens and vapour phase reflow systems on the market that generate a negative pressure or vacuum during the liquid phase, which ‘sucks’ the gas bubbles out.

The voiding can be avoided by adjusting the temperature profile. A zone of constant temperature is then created below the melting temperature of the solder. This allows the outgassing solder flux to escape without immediately becoming trapped in the liquid tin. Depending on the type of solder paste, this method has more or less effect.

Solder paste

Solder pastes can be specially designed and formulated to reduce outgassing. These solder pastes will, under the same conditions, show far fewer voids than standard solder pastes.

Interflux® DP 5505 solder paste is a low voiding solder paste. With GlobalPoint PTP reflow trackers and software, recording and adjusting temperature profiles becomes child’s play.

More info?

Leave your details via the contact form and we will contact you as soon as possible!

– Written by Bart van de Lisdonk

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