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Short R.,Photo Stencil LLC
SMT Surface Mount Technology Magazine | Year: 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.


Miller-Short R.,Photo Stencil LLC
SMT Surface Mount Technology Magazine | Year: 2015

A study is performed to explore whether a single-thickness electroform stencil can print flux or solder paste into a recessed area on a PCB for an embedded flip-chip with a cavity depth of 14 mils. a reservoir was created on the front side of a PCB by gluing a 356 μm thick shim on the flex circuit. Flip-chip pads were embedded in the cavity. The shim was pin registered to the flex and then glued in place. For the stencil, a 2 mil thick 3D electroform stencil was used with a 14 mil deep pocket and apertures consisting of 10 mil circles. The stencil was grown on a mandrel with pocket walls that were machined at 45°. For reservoir printing, the squeegee blade of choice is either a contained head pump-print system or a pump-print rubber blade. The results show, as with step mode printing, that the type of squeegee blade used makes a difference. The stencil results also depended on the stencil zone and aperture size. The different zones produced vastly different results. The study shows that a rubber-pump squeegee blade is necessary for flux to transfer out of the reservoir onto the substrate flip-chip pads.


Miller-Short R.,Photo Stencil LLC
SMT Surface Mount Technology Magazine | Year: 2014

Rachel Miller-Short informed on how efforts were made to print two-level PCBs in one step with a 3D electroform stencil. He participated in a set of experiments, which determined if a 3D electroform stencil could be used in one printing step to print a two-level board with cavities. The tests consisted of printing flux and solder paste into a recessed area on a PCB for an embedded flip-chip with a cavity depth of 14 mils. The printing tool used was a single thickness 4 mil thick 3D electroform stencil with apertures consisting of 10 mil circles. Printing was done in two modes, such as a step mode for the two levels and a reservoir mode for the recessed pocket.


Miller-Short R.,Photo Stencil LLC
SMT Surface Mount Technology Magazine | Year: 2014

A customer was trying to print solder fillets on gold Kovar tabs. The tab was finish plated with 150 inches of nickel and then over-plated with 100 inches of gold. When the component was attached, the solder fillet needed to align precisely with the tab and the solder reflow had to be perfect. When the component was attached, the solder fillet needed to align precisely with the tab and the solder reflow had to be perfect. For this demanding application, there could be no gas pockets or voids anywhere on the fillet, which meant that ensuring sufficient venting for flux residue from under the part was a priority. The plan was to use machine placement for a more accurate and repeatable result and to speed throughput to accommodate increasing volumes. The solution included two important elements an aperture design that employs a honeycomb type structure, and ground plane aperture designs for quad flatpack no-lead (QFN) stencil printing, which solves a similar problem with small part attachment with a large ground attachment.


Short R.,Photo Stencil LLC
SMT Surface Mount Technology Magazine | Year: 2014

The electroformed stencil and its fabrication have a great influence over the ability of the circuit board assembly manufacturer to reliably reproduce the desired depositions necessary for paste application. Stencils can be laser cut with or without post-processing, which for many applications is sufficient to get the paste application process completed reliably. The roughness of the stencil wall is one of the major influences on how well paste will release from the stencil. The rougher the sidewall of the aperture, the more the paste is prone to sticking onto the edge of the wall. One handy predictor of the stencil's ability to effectively transfer solder paste is the area ratio. The area ratio is defined as the area of the aperture opening divided by the area of the aperture side walls. Creating the stencil through the electroforming process has the advantage of keeping the inside release edge of the stencil perfectly smooth.


Miller-Short R.,Photo Stencil LLC
SMT Surface Mount Technology Magazine | Year: 2014

Although selecting a frame is important, and there are several options that should be considered, if you have a reputable stencil manufacturer, the chances of choosing the wrong coupled with the frame request and other details, are usually standard procedures for new stencil customers and on most orders. However, using the wrong frame can either directly affect the print and gasketing of the stencil or it will deem the stencil un-usable as it won't mount or fit into the printer. Yes, the printing process truly is complex. The frame is an important consideration and one you should think about when you initially select your stencil. With a little forethought and some help from your printer or stencil manufacturer, you can look forward to a successful printing process.


Miller-Short R.,Photo Stencil LLC
SMT Surface Mount Technology Magazine | Year: 2014

Rachel Miller-Short provides recommendations for improving stencil printing results. There are various causes of poor print performance. The problem may stem simply from an inferior or worn-out stencil, which is typically the first place people focus when troubleshooting. However, the issue may also be caused by an improper aperture design or stencil thickness. To find the cause of the problem, it is helpful to break the stencil printing process into two phases. The first is the fill phase, when the aperture is filled with solder paste. The second phase is the transfer process, during which the paste is released from the aperture and transferred to the pad on the PCB. The printer must make sure his stencil is an optimal one for his application and is designed with the apertures and the area ratios that you need. He must check the equipment and the board support the squeegee blades, the printing process, and must not forget to consider the solder paste he is using.


A method is disclosed for electroforming metal screen. The method deposits photoresist over a mandrel, and then exposes the photoresist with light through a plurality of openings in a photo tool to form hardened resist pillars. Unexposed photoresist is removed without affecting the resist pillars. The method then electroforms the metal screen in areas free of the hardened resist pillars such that the metal screen forms apertures defined by each of the resist pillars, a space between at least two of the resist pillars defining a support bar that forms at a reduced thickness as compared to portions of the metal screen that are not between the resist pillars. Finally, the method detaches the metal screen from the mandrel.


Trademark
Photo Stencil LLC | Date: 2015-08-25

Stencils used in the production of electronic circuit boards and other electronic components.


Trademark
Photo Stencil LLC | Date: 2016-04-05

Stencils used in the production of electronic circuit boards and other electronic components.

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