Assembly DFM Guidlines

Download the DFM Guidlines PDF

R&D Assembly provides quick turn manufacturing for companies that demand high quality manufacturing, short-run, low-volume of high-value electronic assemblies. We intend to help you produce your designs to your specifications and industry standards, as quickly as possible. If your company develops, designs, and markets electronic products, R&D Assembly is positioned in the industry to support your business objectives in the fastest time to market possible.

Manufacturing of an electronic assembly involves a number of operations that seem to take place in a linear sequence, one step followed by another in step. It is obvious that you cannot place parts in solder paste until after you have printed, nor clean until after soldering. If we carry out the entire process in a linear sequence, not beginning one step until the preceding step is completed; it would take many days or weeks to produce an assembly.
R&D Assembly can cut that time down to the minimum possible, and help drastically improve your time to market; with a bit of advance assistance from you.

The critical path for assembly rarely requires more than an hour or two. The fact is that printing paste on a board takes a matter of seconds. Machine placing parts requires only a few minutes as does soldering and cleaning. If we want to complete the process as quickly as possible we must plan and setup to complete the process steps concurrently. In order to make this reality work for you, we need to share some knowledge with each other. Please take a few minutes to review this guide for what can streamline the process on our side. In the end, your careful attention to this information may save you time and money; it may be the difference between success and failure. Feel free to discuss any of the guidelines, via email, phone or drop by for a face to face, in the factory, discussion at any time.

Production Planning / Quoting

We plan production during the quote cycle. When offering deliveries as quickly as 1 day advance information becomes of primary importance. With proper experience and documentation it is possible to produce a reasonably accurate quote without enough information to produce your product. We find this method of quoting, while responsive to the needs of your delivery times and deadlines, may not encourage concurrent manufacturing. Getting good information up front establishes good lines of communication, ensures an accurate quote and enables us to begin process development even before you complete the PO.

Bill of Materials
We work with MS Excel and can handle your material list in most standard spreadsheet formats. We can merge data from multiple sources but ultimately we need the following information:
Component description; e.g. capacitor, resistor inductor, IC; value, voltage, type, foot-print, JEDEC number
Manufacturer and manufacturer’s part number
Reference Designators; associate Component Type with components of the assembly
Component Locations
associate Reference Designators with locations on the assembly, centroid data usually derived from CAD.
We can derive the centroid data from data used to produce the board, Gerber Files. But, it will slow us down (required for machine programming).
Assembly Drawings
The drawing should show where the parts are located on the assembly. Special notes / modification: Frequently, these are included on the drawing but we also work from text files and photos. We are perfectly satisfied with PDF of these type documents.
CAD Files
Schematics, Board Design Artwork, Gerber Files. We need software files of this type to generate process documentation and machine program files for the manufacturing sequence.

Purchasing considerations

Surface finish
Purchase part designed for soldering. PbFree terminations are fine, but Pd and PdAg finishes on leadless devices must have a barrier layer to prevent leaching of the terminal. If you are not sure, please ask.
Presentation media
If we quoted your job for machine assembly, and you are providing parts in kits, they must be in tubes, trays, or tape & reel. We have a limited ability to handle bulk parts and cut tape on the machines.
Hand assembly allows more flexibility
Beware electronic components can be fragile and susceptible to damage from handling, ESD and moisture absorption. Do not remove components from protective packaging. We will return unused parts in their protective media once your job is complete.
Turnkey
We a selective stockroom based upon the requirements of our core customer base. We carry some components with long purchase lead times for them as well. We purchase through distribution from Allied, Arrow, Avnet, DigiKey, Mouser, Newark, etc. If you provide us with distributor’s part numbers we will attempt to purchase materials using your information. If you provide manufacturer’s part numbers we will search for those specific materials. If you provide generic descriptions we will search for materials using your descriptions. Obviously, good information will reduce the time and cost of producing your products.

Receiving Considerations

We check the work of our suppliers. If you provide us with kits for assembly you become a supplier at this point. You can help. Clearly mark the kit with additional information you use to assemble the kit. We may be able to use the information to check your work.

Assembly Setup

We begin to organize your kit for assembly during the receiving inspection process. We sort the kit by component type, assembly sequence, and associate your parts with design reference designators. We organize the components by process step and assembly sequence step.

Solder Paste Printing

You can reduce the time and cost by including a solder paste layer in your CAD design.
The stencil apertures should, generally speaking, be no larger than the land pattern within the opening in the solder mask. The IPC-7525 Standard provides guidelines for stencil design.
Our automated printer requires a 20” x 20” stencil frame. It may be possible to order a single stencil with two or more images in the work area, which is about 16” by 18” inches. Images within the work window must be separated by about 1.5”.
If you choose to have us purchase a stencil for you, we will specify the thickness of the stencil based on the type of components used and your end-item requirements (Service Environment and IPC Product Class).
Your board should include fiducial marks; at least two of them, as far apart as possible on the board or panel. The IPC-2221 provides guidance. In addition, you should include 0.125” unsupported tooling holes on the board. These will be used to register the board to the printer bed and stencil.

Dispensing

We have a simple time-pressure dispenser. Typically, we use it to dispense temporary solder mask. Occasionally, we may dispense adhesives or solder paste. This machine does not require any additional information than we have previously requested.

Component Placement

Automated placement equipment requires us to develop a software routine to run the machine. We need the information as requested for quoting. If you can provide the information directly from your CAD files it is best.
We must have parts in presentation media appropriate for the machine feeders and pick nozzles.
We must have all of the information requested for quoting. We may be able to develop much of the necessary information piecemeal using various CAD tools and other software but these methods are time consuming, costly, and compromise the process output to varying degrees.
The fiducials used to align the stencil to the board will generally be adequate for placement. However, if your design employs fine pitch components (less than 0.5 mm pitch) we recommend local fiducials for these components.

Reflow Soldering

We know your time is limited but to give you the best possible product we need your help. We must develop a Time / Temperature Profile for your board and our process materials (solder, flux and cleaning process). From that profile we establish oven and conveyor settings, a recipe to solder the assembly without damage. We use water soluble fluxes. We have a variety of solder paste formulations at our disposal to ensure process results that meet your end product requirements.

Manufacturer and Manufacturer’s Part number, data sheets in electronic form if you have them.

Through Hole Installation

We employ a variety of automated lead forming equipment. This equipment requires leads to be straight.

The equipment works best with axial lead components on tape.

Wave Solder process considerations

Our conveyor is an edge finger chain. It clips the edge of the board to ensure proper exposure to the fluxer and solder wave.

Component placed very close to the board edge may be in the shadow of a finger, or prevent installation of the stiffener-dam.
Edge connectors that overhang the board are incompatible with these fingers. We may need to produce or purchase a pallet for your board. We may simply choose to hand solder these components after wave soldering. You may be able to eliminate these issues by requesting boards in a break away panel.
Components that cannot withstand cleaning cannot be wave soldered (in this shop). We use a water soluble flux in a foam fluxer. This provides us with a very wide process window. The flux must be cleaned from the board after soldering.

Hand Soldering considerations

Assembly designs with 0402 and larger components present the practical limit for hand soldering. We have assembled products with significant numbers of 0402 chip capacitors and resistors by hand. Smaller than tah will require special equipment.
Components that cannot withstand the rigors of reflow, wave solder or aqueous cleaning must be hand soldered, with low residue flux.

Cleaning Considerations

We use have an Aqueous Technologies CL400 cleaner. It is a closed loop (no drain) DI water washer. Water is heated to 120 degrees F and purified using a carbon and mixed resin bed. We may not be able to clean in the gap between very small components. We use IPC guidelines to evaluate the feasibility of cleaning under components.

We should evaluate your design before ordering a solder paste stencil. If we need to install a component after cleaning, using low residue flux we may choose to close some apertures in the stencil layer.

Inspection considerations

We build and inspect using best manufacturing practices described in IPC J-STD-001. This standard presumes components, materials, designs, tools and methods conform to a number of other IPC standards. These standards are extensions of the J-STD-001.

When components, materials, designs, tools, or methods do not conform to the standards, the end result may not conform to the acceptance criteria described in the J-STD-001. We will contact you to establish acceptance criteria. This of course, takes time and money. Make every effort to ensure that your design conforms to IPC-2220 series of Design Standards.
If you specify special components or technologies in your assembly, establish acceptance criteria and document the criteria on your assembly drawings or special instructions.

Rework – Repair

We, in accordance with the J-STD-001 and other IPC standards monitor defects and rework.

We do not make repairs without your knowledge and agreement on method. If repair is required we will recommend and IPC-7721 repair / modification method. You may accept, recommend or reject based on your needs.
We assemble products on a best effort basis. We accept responsibility for the cost of the materials in the product. We accept no liability beyond the cost of the materials in the assembly.

Packing and Shipping

We will package your product for shipment or hand delivery, as agreed on in the PO. The material will be protected from damage in normal shipping and handling, based on information provided to us by you.
Product will be insured during shipping as requested on the PO.