Adapting Stencils to Manufacturing Challenges in 2015

Now that we're well into 2015, we can take a look back at the 2014 stencil market and explore our expectations for 2015.

In general, 2014 was a solid year with year-over-year growth in volume. Component sizes continued to get smaller, with 01005 components no longer a rarity, but a regular occurrence. Shrinking components have been accompanied by shrinking spaces between the components. This combination of small components and spacing constraints has continued to challenge stencil manufacturers. Combine that with boards that contain both 01005 components and standard size components, and the stencil manufacturers have had to head back to the lab to find ways to accommodate these challenging parameters.

In the solder paste printing process, the squeegee blade delivers solder paste into the stencil aperture as it travels across the stencil surface. When the board separates from the stencil the solder paste in the stencil encounters a competing process: solder paste will either transfer to the pad on the PCB or it will stick to the inside of the aperture walls. The smaller the area ratio (the area of the aperture opening divided by the area of the inside aperture wall; the generally accepted guideline is area ratio > .45, depending on technology), the more difficult it is to achieve complete paste release.

To achieve good paste release with apertures small enough to accommodate 01005 components, manufacturers have experimented with different stencil materials and technologies. The material the stencil is made from determines the size of the aperture and the smoothness and exactness of the aperture walls. The need to satisfy the more rigorous printing requirements of finer pitch components leads to a natural hierarchy of stencil technologies based on the application.

The hierarchy advances through the technologies, starting with laser cut and reaching to electroformed and electroformed NiEx stencils, which are used for very fine pitch SMT and wafer bump applications. It was discovered that the smoother walls associated with electroform stencil technology provide better paste transfer and that good paste transfer can be achieved at lower area ratios. The electroformed product lines can address additional application needs such as .1 mil increments in stencil thickness requirements. In fact, good paste transfer has been achieved with area ratios as low as .42 with electroformed stencils.

For 2015, we will see the gamut of stencil types. Laser cut stencils will be used for more R&D and simple low-volume products where the components are larger; the solder paste deposit doesn’t have to be as exacting, and where the boards are relatively uniform. Laser cut stencils have become quite commercialized and can be purchased in many places at a relatively low price. They fill the need for companies that want off-the-shelf stencils they can get quickly.

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Editor's Note: This article originally appeared in the March issue of SMT Magazine.

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2015

Adapting Stencils to Manufacturing Challenges in 2015

04-08-2015

Rachel Miller-Short reviews the stencil industry in 2014 - including market growth, technology developments, and challenges - and talks about what to expect and new trends happening this year.

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The Short Scoop: Stencil Printing in PCB Cavities

01-14-2015

Reservoir flux and solder paste printing can be done in one step with a 3D electroform stencil, but additional studies and techniques need to be explored to achieve the best result.

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The Short Scoop: Printing Two-level PCBs in One Step with a 3D Electroform Stencil

01-06-2015

The requirements for two-level PCBs with components on both levels have seen a recent increase. Stencil printing on both levels requires special stencil and squeegee blade designs. Recently, Columnist Rachel Miller-Short participated in two experiments. The purpose was to determine if a 3D electroform stencil, in just one printing step, could be used to print a two-level board with cavities.

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2014

Improving Stencil Printing Results

10-03-2014

A myriad of causes can result in poor print performance. The problem may stem from an inferior or worn-out stencil, but the issue may also be caused by an improper aperture design or stencil thickness. Poor print performance might not be caused by the stencil itself, but rather an improper printer set-up, a non-optimal squeegee blade, or the rheology of the solder paste being used.

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The Short Scoop: Improving Stencil Printing Results

09-24-2014

A myriad of causes can result in poor print performance. The problem may stem from an inferior or worn-out stencil, but the issue may also be caused by an improper aperture design or stencil thickness. Poor print performance might not be caused by the stencil itself, but rather an improper printer set-up, a non-optimal squeegee blade, or the rheology of the solder paste being used.

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More Stencil Questions (and the Answers!)

09-05-2014

Rachel Miller-Short's March column, "10 Common Stencil Questions," brought in a slew of new questions from readers. In this edition of "The Short Scoop" she addresses a few of those inquiries. Take a look: Do you know the answers?

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The Short Scoop: More Stencil Questions (and the Answers!)

07-30-2014

Rachel Miller-Short's March column, "10 Common Stencil Questions," brought in a slew of new questions from readers. In this edition of "The Short Scoop" she addresses a few of those inquiries. Take a look: Do you know the answers?

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Selecting a Stencil Frame

07-02-2014

One part of stencil selection that is often overlooked, but is also quite necessary, is the selection of the frame. This month's column from Rachel Miller-Short takes a look at the stencil frame and the options to consider when specifying the frame required for your printing process and needs.

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The Short Scoop: Selecting a Stencil Frame

07-02-2014

One part of stencil selection that is often overlooked, but is also quite necessary, is the selection of the frame. This month's column from Rachel Miller-Short takes a look at the stencil frame and the options to consider when specifying the frame required for your printing process and needs.

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Screen Printing Solutions for Small Die & Precision

05-14-2014

As discussed in previous articles, when selecting stencils, the trick is choosing the right tool for the right job; but sometimes the need for tailoring a stencil for a specific application can take a bit more engineering time and several iterations to get the desired results.

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The Short Scoop: Screen Printing Solutions for Small Die & Precision

05-14-2014

This month, Columnist Rachel Miller-Short discusses one of her more demanding customer applications. As discussed in previous articles, when selecting stencils, the trick is choosing the right tool for the right job; but sometimes the need for tailoring a stencil for a specific application can take a bit more engineering time and several iterations to get the desired results.

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10 Common Stencil Questions

04-16-2014

There are a wide range of stencils and stencil technologies available and many questions arise when the time comes to select one. This month’s The Short Scoop answers the 10 most common questions our customers ask.

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The Short Scoop: 10 Common Stencil Questions

04-16-2014

Today a wide range of stencils and stencil technologies are available and many questions arise when the time comes to select one. Stencil users who optimize the correct stencil technology for their specific application and processing parameters enjoy greater yields and significantly lower rework. As always, it is about selecting the right tool for the job.

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2013

The Short Scoop: Stencils for QFNs

11-20-2013

QFNs present many challenges to the assembly printing process, but the short scoop is that with proper stencil design, correct stencil technology selection (laser, electroform, and nano-coat), and consideration for the effects of PCB soldermask layout choices, these challenges can be overcome.

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The Short Scoop: Step Stencils, Part 2 - Applications and Solutions

10-16-2013

Columnist Rachel Short writes: "In my last column, 'The Ins and Outs of Step Stencils, Part 1,' you heard a little about step stencils--what they are, why demand is increasing, different types, and what to look for. In this column, we explore step stencil applications and solutions."

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The Short Scoop: The Ins and Outs of Step Stencils

09-11-2013

Today, fine-pitch components, which necessitate a thin stencil for acceptable paste release, are sandwiched beside a variety of devices and components that require higher paste height. Getting the solder paste volume needed for larger components, while still having an area ratio that allows for good paste release on small components, can be challenging.

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The Short Scoop: Squeegee Blades

07-03-2013

One often overlooked component of the soldering process is the squeegee blade, which is critical in solder paste application. The technology of the seemingly simple squeegee blade is as important as the stencil when it comes to the printing process. The application, type of stencil, and the printer set-up should all be determining factors in selecting the blade.

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The Short Scoop: Introduction to Stencil Printing

06-19-2013

Many different types of stencils are available today from many different suppliers, but not all stencils are created equal. And because the industry operates in a quick-turn, dynamic environment, industry lead-times for delivery, in many cases, are as important as the stencil's capabilities.

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