Patent Description:
Pallets such as selective wave soldering pallets are used to build printed circuit boards (PCBs). These PCB pallets provide a template to help install through hole components on the PCB during assembly. Additionally, PCB pallets protect surface mount components and provide unmasked areas for wave soldering. These PCB pallets are typically made by a hand lay-up process that starts with a glass fiber-embedded thermo-setting sheet. The sheets are stacked one on top of the other, to form a tray. The tray is then put under pressure and elevated temperatures to cure the thermosetting polymer. Often, the tray for the pallet may need to be cut using a computer numeric control (CNC) cutting system to make all the holes and slots needed for the particular PCB layout.

Serving as the template for the circuit design, PCB pallets are subjected to cyclic heat from soldering, and impact and chemicals from component installation. Because of this relatively harsh environment, PCB pallets tend to wear down relatively quickly and need replacing.

More specifically, when in use, the pallet and PCB are placed in a bath of solder which adheres to the PCB through the holes and slots in the pallet. A variety of cleaning agents and other chemicals are then applied to the PCB while on the pallet. It is, therefore, easy to see how these pallets wear down over time and need to be replaced. Replacement is an issue, however, since these pallets are expensive and take a relatively long time to make. Being handbuilt and require substantial CNC time to create the final design of the pallet results in a multiweek turnaround time. Such PCB pallets are highly specialized to each particular PCB, so waiting for pallets made according to current methods might stop or delay a surface mount technology PCB manufacturing line.

Conventional printed circuit board pallets are known from <CIT>, <CIT> and <CIT>. A method for 3D printing of objects using thermoplastic powder is disclosed in <CIT>.

The present invention is defined by the appended claims and includes building a PCB pallet through an on-demand additive manufacturing process rather than using conventional hand lay-up, or other processes. Illustratively, the on-demand method of making a new PCB pallet may include providing an inorganic sheet stock for the base. Using a printing-type process, a controlled spray of fluid is applied onto the base at selective locations where the pallet will be built-up. After the fluid application, a polymer powder is deposited onto the sheet stock at the locations sprayed with the fluid. The excess powder is removed and the process repeated as necessary to form stacks that creates the PCB template on the pallet. The pallet is then put under pressure and heated to fuse the polymer powder to form the completed final PCB pallet. In the present invention the fluid is a coalescing agent comprising monomers or oligomers of the polymer powder.

An embodiment of the present invention provides a method according to claim <NUM> of the appended claims.

In the above and other embodiments, the method of making a printed circuit board pallet may further comprise: the inorganic sheet stock including randomly oriented fibers made from a material selected from the group consisting of glass and carbon; the fluid being printed onto the inorganic sheet stock at that selective locations based on a design of a printed circuit board; the fluid being a volatile fluid; the step of applying the fluid is accomplished using a method selected from the group consisting of inkjet, spray nozzles, rollers, and stamps; the polymer powder that is deposited onto the base at the selective locations applied with the fluid being selected from the group consisting of at least one of a thermoplastic powder, thermoset powder, nylon, polyethylene, polyether ether ketone; the excess amounts of the polymer powder being removed by a mechanism selected from the group consisting of blown compressed air, vacuum, vibration, and agitation; the step of repeating the steps of providing another base in a form of an inorganic sheet stock; applying another fluid onto the base at selective locations on the another base to build-up the pallet in three-dimensions; depositing additional polymer powder on to the another base at the selective locations applied with the another fluid; and removing any excess amounts of the another polymer powder not adhered to the another fluid before heating the pallet; the pallet being heated in a thickening oven; and the oven temperature being about <NUM> degrees Fahrenheit and above (corresponding to <NUM> and above). In an illustrative example which is not part of the present invention, a method of repairing a printed circuit board pallet is provided, the method comprising the steps of: providing an existing but damaged printed circuit board pallet; applying a fluid onto the damaged printed circuit board pallet at selective locations where the damaged printed circuit board pallet will be built-up; depositing a polymer powder on to the damaged printed circuit board pallet at the selective locations applied with the fluid; removing any excess amounts of the polymer powder not adhered to the fluid; and heating the damaged printed circuit board pallet to fuse the polymer powder together and to the base.

In the above and other embodiments and illustrative examples the method of making a printed circuit board pallet may further comprise: the step of applying the fluid which is accomplished using a method selected from the group consisting of inkjet, spray nozzles, rollers, and stamps.

The exemplary apparatuses, systems, and methods shall be described hereinafter with reference to the attached drawing which is given as a non-limiting example only, in which:.

The figures and descriptions provided herein may have been simplified to illustrate aspects that are relevant for a clear understanding of the herein described apparatuses, systems, and methods, while eliminating, for the purpose of clarity, other aspects that may be found in typical similar devices, systems, and methods. Those of ordinary skill may thus recognize that other elements and/or operations may be desirable and/or necessary to implement the devices, systems, and methods described herein. But because such elements and operations are known in the art, and because they do not facilitate a better understanding of the present disclosure, for the sake of brevity a discussion of such elements and operations may not be provided herein.

For example, as used herein, the singular forms "a," "an" and "the" may be intended to include the plural forms as well, unless the context clearly indicates otherwise.

When an element or layer is referred to as being "on," "upon," "connected to" or "coupled to" another element or layer, it may be directly on, upon, connected or coupled to the other element or layer, or intervening elements or layers may be present, unless clearly indicated otherwise. In contrast, when an element or layer is referred to as being "directly on," "directly upon," "directly connected to" or "directly coupled to" another element or layer, there may be no intervening elements or layers present. Further, as used herein the term "and/or" includes any and all combinations of one or more of the associated listed items.

Yet further, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section.

The present invention is directed to building a PCB pallet on-demand using additive manufacturing rather than using conventional hand lay-up, or other processes. The on-demand method of making a new PCB pallet may include providing a polymer sheet stock for the base. Using a printing-type process, a controlled spray of fluid is applied onto the base at selective locations where the pallet will be built-up. After the fluid application, a polymer powder is deposited to the sheet stock at the locations sprayed with the fluid. Any excess powder is removed and the process is repeated as necessary to form stacks. These stacks form the PCB template on the pallet. The pallet is then heated and cooled to fuse the polymer powder together forming a completed PCB pallet. In an embodiment the inorganic base may be either chemically or physically removed, via acid etching, sand blasting, or other like means.

More particularly, an embodiment of a process for on-demand building of a PCB pallet as indicated by reference numeral <NUM>, is shown in <FIG>. The process starts by providing sheet stock that serves as the PCB pallet base, as indicated by reference numeral <NUM>. A coalescing agent is then printed onto the sheet stock at selective locations based on the ultimate design and configuration of the PCB, as indicated at reference numeral <NUM>. After the coalescing agent, a powdered polymer is applied to the sheet stock on the coalescing agent, as indicated by reference numeral <NUM>. Excess polymer powder may then be removed from the sheet stock, as indicated by reference numeral <NUM>. It will be appreciated by the skilled artisan that the excess polymer resides at locations not printed with the coalescing agent at <NUM> to be removed. With the excess polymer removed, the process may be repeated wherein stacks of multiple sheets can be placed on top of each other, as indicated by reference numeral <NUM>. This builds-up the three-dimensional shape on the pallet needed for the PCB template. Once this is done, the stacked sheets are placed into a thickening oven and heated, as indicated by reference number <NUM>. This fuses the applied polymer powder. The pallet is then removed from the oven as indicated by reference numeral <NUM>. Any additional loose polymer can then be removed, and the pallet trimmed as necessary to complete the on-demand build process.

As indicated, the starting point in this embodiment is providing the sheet stock base that will be used as the foundation to build-up the PCB pallet design. Illustratively, the sheet stock may be either a glass or carbon fiber mat that can be cut to the desired size and shape as needed pallet.

With respect to applying the liquid pursuant to the step identified by reference number <NUM>, a coalescing agent is applied to the sheet stock. The fluid is a coalescing fluid comprising monomers or oligomers of the polymer powder to be applied to the sheet stock. According to illustrative examples, which are not part of the present invention, the applied liquid may be a volatile fluid such as water, water with <NUM>-pyrrolydone, glycols, oils, surfactants or combinations thereof. It is further appreciated, that applying the liquid may be done by a variety of printing or depositing mechanisms such as inkjet heads and nozzles, rollers, stamps, etc. The point is the fluid is deposited according to a predefined design based on the structural characteristics needed for the final PCB pallet.

With regard to the polymer powder application step identified by reference numeral <NUM> in <FIG>, the powder polymer is applied on the sheet stock at the locations defined by the fluid application. The powder, therefore, adheres to the liquid on the sheet stock. It is appreciated that suitable polymer powders may include thermoplastic or thermoset powders, nylon, polyethylene, polyether ether ketone (PEEK), polyaryl ether ketones to include Polyketone, polyether ketone, polyether ketone ketone, polyether ether ketone, polyphenylene sulfide, polyphenylen sulfone, polyether sulfone. Polyamideimide, polyimide or copolymers thereof and alloys thereof. It is further appreciated that with these and other like polymers, the particle size and distribution may be used to control the characteristics of the resulting raised layers formed on the sheet stock.

To create the desired shape that the polymer is intended to make, any excess powder polymer needs to be removed according to the step indicated by reference numeral <NUM> of <FIG>. It is appreciated that the powder may be removed by any variety of means such as blown compressed air, vacuum, vibration, agitation, etc. The objective being that all the loose powder is removed from locations on the sheet stock not specifically deposited with the fluid.

After the polymer is applied and the excess removed, this process may be repeated to the extent needed depending on the design of the PCB template. The point of adding the layers on the sheet stock is to create the three-dimensional body in the configuration needed to create a PCB. Accordingly, the above process is repeated with the polymer and sheets stacked on top of each other to the extent necessary to make the appropriate three-dimensional shape.

Once the stacks are built from the step at <NUM>, they may be placed into an oven to fuse the powder to form the final structure. Here, the powder heats and fuses the particles to each other and to the sheet stock. In addition, the applied coalescing agent evaporates during this heating step. It is also appreciated that the liquid may be removed through other means depending on the type of liquid used, the polymer applied, and the curing means. Furthermore, the temperature and duration in the oven will depend on the polymers used for the powder and sheet stock, as will be contemplated by the skilled artisan. An illustrative temperature may be above about <NUM> degrees Fahrenheit (corresponding to ca.

Once the pallet is solidified and removed from the oven, any remaining polymer powder or excess fused powder may be trimmed or removed by means known to the skilled artisan. Also, the inorganic sheet stock is removed. After this clean-up step, the pallet should be fully formed and ready for use in production - hence and on-demand PCB pallet.

Using this on-demand additive process, the time needed to make a replacement pallet can be shortened from <NUM>-<NUM> days to the same day. No longer is a time-consuming hand build-up process needed to create the PCB pallet. Also, the CNC time is reduced and possibly, in some cases, eliminated. It may also be less expensive and provide direct control over the pallet build process. This translates into shorter lead times for making any PCBs which may reduce the risk of a surface mount technology PCB manufacturing line shutting down to wait for new pallets.

According to an illustrative example, a method includes extruding a thermoplastic sheet stock and then overprinting the necessary features using a fused deposition molding (FDM) style printer to make PCB pallets. A simplified flow chart depicting this alternate method of making a PCB pallet, as indicated by reference numeral <NUM>, is shown in <FIG>. Illustratively, a plurality of sheet stock is extruded at a nominal sheet thickness of about <NUM> mils (<NUM>), as indicated at reference numeral <NUM>. The sheets are then run through a FDM printer to print the selective build locations, as indicated at reference numeral <NUM>. The FDM printer essentially over-molds the damming features on the pallet. This keeps the solder material away from the non-soldered portions of the PCB. It is appreciated this process can be employed with the CNC printer to make all the cuts into the pallet base for the solder locations, as indicated at reference numeral <NUM>.

Claim 1:
A method (<NUM>) of making a printed circuit board pallet, the method (<NUM>) comprising the steps of:
Providing (<NUM>) a base in a form of an inorganic sheet stock;
Applying (<NUM>) a fluid onto the base at selective locations where the pallet will be built-up to a three-dimensional form;
depositing (<NUM>) a polymer powder on to the base at the selective locations applied with the fluid;
removing (<NUM>) any excess amounts of the polymer powder not adhered to the fluid; and
heating (<NUM>) the pallet to fuse the polymer powder together and to the base, wherein the fluid is a coalescing agent consisting of monomers or oligomers of the polymer powder.