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The most neglected manufacturability design concepts

If you are coming across recurring in process defects, manufacturing bottlenecks, or excessive rework, a manufacturability design review can make a serious change to your manufacturing costs and defect rates.

We have compiled a list of the most neglected manufacturability design concepts for reducing costs and eliminating rework:

#1: Incorrect pad sizing and spacing. Whether 0201's or ultra fine pitch IC's, pad size and spacing is king. We have found that tombstones (SMT components standing up on one leg within the oven) are almost always corrected by altering pad sizes and spacing, especially for smaller components like 0201's. The leg of a component needs to be pulled down by a solder joint concaving at the perfect slope. Altering size and spacing of pads for the legs of ICs not only reduces bridges and possibilities for shorts, but allows for lower cost bare board manufacturing processes—explained in #3.

#2: Placing through hole components on both sides of an assembly. Often times the simplest assemblies are the hardest to assemble if improperly designed—this results in higher manufacturing costs. If surface mount components are placed on both sides of a board, they will either have to be masked to allow for wave soldering of through hole components, or the through hole components will have to be hand or selective soldered. If through hole components are placed on both sides of a board, one of the sides will have to be hand or selective components.

#3: Spacing and positioning of traces, via's and pads. Usually the part of an assembly that has the greatest potential for reducing raw costs with the smallest change in design is the bare board. Sometimes using higher quality board houses with higher cost manufacturing processes can be avoided by altering the spacing between copper on a board. Board houses employ different manufacturing processes which have certain tolerances for what they can produce efficiently. Sometimes the traces on a board can be spaced apart enough that a cheaper process can be used, resulting in major cost savings for an OEM. A few small tests can be done on the Gerber files for a board which will reveal all traces and via's with tight tolerances.

#4: The importance of clear PCB fabrication specifications. Many times board houses get only one copper callout for fabrication.  However in the manufacturing process for any external copper layer, there is a starting copper value and a finish copper value.  It can be critical to have the proper finished copper weight to carry your assembly's power characteristics.  When designers only state 1 oz Cu, some board shops will take this requirement as starting copper and finish the board at 1.5-2 oz Cu, and others will take this as a finish requirement and start your board at .5 oz Cu and finish at 1 oz Cu.  If your intent was a starting copper value, the board produced finishing at 1 oz Cu may pass testing, yet fail in the field prematurely.

#5: Allowing proper spacing between components. Many designers pack SMT components tightly together in order to conserve space. It is important to maintain a minimum spacing between components. Components need enough space on their own pads to auto-align within the paste—it is never a good idea to share pads between components.

#6: Panelization. Bare board assembly houses look to panelize your product for optimum speed and accuracy as well as reduce waste by fitting the most boards possible onto their production panels. It is best to allow your electronics contract manufacturer to panelize your boards for you. The contract manufacturer knows the board house's optimal panelization for reducing waste and increasing production efficiency. Proper panellization also ensures efficient depanelization and effective wave soldering.

With Profab's extensive experience in manufacturing we can review your product before you go to prototype. You can make the required changes to eliminate the design errors that lead to costly boards that are hard to manufacture and do not run as efficiently through production. These changes speed production and lower cost and ensure rapid delivery to market. With Profab's cost advantage with our Blank PCB manufacturers we can significantly lower your printed circuit board costs and speed manufacturing through efficient panelization.

Profab can assist you in addressing all of the above issues and more as well as migrating boards from more labor intensive through hole boards to machine efficient surface mount boards.