For electronic circuit board designers , especially designers, product design for manufacturability (Design For Manufacture, referred to as DFM) is a factor that must be considered , if the circuit board design does not meet the design requirements for manufacturing , will greatly reduce production efficiency , severe cases can even lead to the design of products simply can not manufacture it. Currently through-hole technology (Through Hole Technology, referred THT) is still in use , DFM in terms of improved efficiency and reliability through-hole can play a significant role in the manufacture , DFM methods can help through-hole manufacturing to lower defects and remain competitive .
This article describes some of the through-hole and related DFM methods essence of these principles are universal, but not necessarily applicable in any case , however , for PCB designers and through-hole technology and engineers to deal stating that there are still some help .
1 , typesetting and layout
Proper layout design stage to avoid many of the manufacturing process cumbersome .
( 1 ) with a large board can save the material , but because of warping and weight reasons, in the production of transportation would be more difficult , it needs to be fixed with a special fixture , so you should avoid using more than 23cm × 30cm of the board . Best of all size control board within two or three of which helps to shorten the adjustment at the time of product replacement rails, re- placing the barcode reader downtime caused by location and the type of board size can be less reduce the number of wave soldering temperature profile .
( 2 ) in a board house contains different kinds of puzzle is a good design , but only those who do a final product in the production process requirements and have the same board can be designed .
( 3 ) around the border of the board shall provide , in particular, when the edge of the plate element , most automated assembly equipment required for the reserved area of at least the side panels of 5mm .
( 4 ) as far as the top surface of the board ( component side ) wiring , circuit board underside ( solder side ) susceptible to damage. Do not place wiring near the edge of the board , because the production process is carried out by grasping the board edge , the edge of the line may be damaged jaw wave soldering equipment or border transmitter.
( 5 ) For devices with higher pin counts ( such as terminal blocks or flat cable ) , you should use the elliptical rather than circular pad to prevent solder when soldering bridge ( Figure 1 ) .
( 6 ) as the positioning hole spacing distance between its larger and components , and standardization and optimization of its size based instrumentation equipment ; Do not do the positioning hole plating, because the diameter of the hole plating is difficult to control .
( 7 ) as far as possible so that the positioning holes are also PCB mounting holes used in the final product , thus reducing the production time of the drilling step .
( 8 ) can be arranged to test the circuit pattern for process control at the edge of the board of waste in the manufacturing process can be used to monitor the pattern surface insulation resistance , cleanliness and weldability , and so on .
( 9 ) For larger board, should stay in the center of a path to a location in the center of the circuit board during wave soldering support to prevent sagging board and solder splatter and help the board unanimously welding .
( 10 ) Consider the needle bed layout design for testability issues should be in , when you can use flat pads ( no lead ) for online testing and better -pin connector , so that all nodes in the circuit can be tested .
2 , positioning and placement element
( 1 ) According to a grid pattern of rows and columns in the form of the position of arrangement of the components , all the components should be parallel to each other axially , so that in the axial direction of the insertion plug installed does not need to rotate PCB, rotating and moving with unnecessary significantly reduce the speed of plug installed . Figure 2, these elements are placed like a 45-degree angle , in fact, can not be inserted by the machine .
( 2 ) similar elements on the plate to be discharged in the same manner . Such as making all the right radial capacitors negative toward the plate , so mark facing the same direction so that all dual in-line package (DIP) gap , which can accelerate the speed of insertion and easier to find errors . As shown in Figure 3, the A board adopted this approach , they are able to easily find reverse capacitors, while the B plate lookup you need to use more time . In fact, a company can be all of its circuit board components manufactured standardized direction , some board layout may not necessarily be allowed to do so , but this should be the direction of an effort.
( 3 ) The dual in-line package devices , connectors and other alignment direction of multi- pin-count devices and wave soldering vertical direction , thus reducing the bridging element between pins .
( 4 ) take full advantage of screen printing on the plate for a sign , for example, draw a box attached to the bar code , printed on an arrow indicates the direction of wave soldering board , with dotted lines delineate the contours underside components ( such printing can be done only once the board ) and the like.
( 5 ) Draw component reference symbol (CRD) and polarity indication , and after insertion elements still visible , which is helpful when checking and troubleshooting , and also a good maintenance work.
( 6 ) from the edge of the board member has to be at least 1.5mm ( preferably 3mm) distance, which will be easier to send the circuit board and wave soldering , and the damage of the peripheral member is smaller .
( 7 ) above the element to be more than 2mm from the plate surface (such as light emitting diodes, high-power resistors, etc. ) , the following should be added to the washer . Without spacers , these elements in the transmission would be " squashed " , and the use of vulnerable to shocks and vibrations .
( 8 ) placed on both sides of the PCB to avoid the elements , as this will significantly increase the time and manual assembly . If the component must be placed underside , it should be physically as close as possible to a complete solder masking tape and stripping operations.
( 9 ) of the element as far as possible evenly distributed in the PCB, it helps to reduce the warp and in the wave soldering heat distribution .
3, the machine Cartridge
( 1 ) All board components pads should be the standard , you should use the industry standard spacing .
( 2 ) an optional component insertion machines should be applied to keep in mind their own equipment within the plant conditions and specifications, packaged in the form of good elements to consider in advance , in order to better fit with the machine . For the profiled element is concerned, the package may be a larger problem.
( 3 ) If possible, try to use the radial component of its axial type , because the axial component insertion cost is relatively low , if the space is very valuable, can also be preferred radial component.
( 4 ) If the board surface only a small amount of axial components , all of them should be converted to a radial type , and vice versa , which can completely dispense with one kind of insertion processes.
( 5 ) when the layout board , from the standpoint of minimum electrical spacing considerations pin bending direction and the automatic insertion of the reach of the installed components , but also to ensure that the pin bending direction does not cause bridging.
4 , the wire connector
( 1 ) Do not wire or cable directly to the PCB, but should use the connector . If the wire must be soldered directly to the board , then use a wire to wire end terminal board terminated . Even from the circuit board out of the wire should be focused on an area of the board , so you can set them together to avoid affecting other components.
( 2 ) Wires of different colors in order to prevent errors during assembly . Each company can use its own set of color schemes , such as high all product data lines in blue , while low in yellow and so on.
( 3 ) should be greater connector pads to provide better mechanical connection , high pin count connectors should be chamfered lead in order to make it easier to insert .
( 4 ) Avoid using dual in-line package socket , which in addition to the extension assembly time , this kind of additional mechanical connection will reduce the reliability of long-term use , and only because of the need to maintain the cause of field replacement when using DIP socket . Today DIP quality has made considerable progress, need frequent replacement .
( 5 ) should be labeled to identify the direction of the carved surface of the plate to prevent errors when installing the connector. Connector solder joints are mechanical stress is more concentrated, it is recommended to use some gripping tools, such as keys and snaps.
5 , the whole system
( 1 ) should be pre- printed circuit board design selected components , so you can achieve the best layout and DFM contribute to the implementation of the principles set forth herein .
( 2 ) avoid the need to use some of the pressure of the machine components, such as wire pins, rivets, etc. , in addition to slow installation , which may damage the circuit board member , and their maintenance is very poor.
( 3 ) using the following method to minimize the use of on-board components Category: instead of a single resistor with resistance row ; with a six -pin connector instead of two three-pin connector ; If the value of the two components is very similar, but different tolerances , the two positions that have a lower tolerance ; plate using the same screws radiators .
( 4 ) preferably designed to be configured in the field General Board . For example, installed a switch used to export domestic plate model , or a model using a jumper into another model .
6 , General Requirements
( 1 ) When the circuit board to do conformal coating , the coating does not need to be part of the engineering design marked out on the map. Design should consider the effect of the coating on the wiring capacitance .
( 2 ) for the through -hole , in order to ensure optimal welding results , and the pin in the aperture of the gap should be between 0.25mm to 0.70mm. Larger pore size of the machine Cartridge favorable , but want to get a good capillary effect is required to have a smaller aperture , therefore need to strike a balance between the two.
( 3 ) shall be conducted in accordance with industry standards chosen pretreatment components. Component preparation is one of the lowest part of the efficiency of the production process , in addition to adding an extra step ( corresponding to the risk of damage and to bring a static delivery extension) , it increases the chance of error.
( 4 ) Most manual deal with the purchase of plug-in component set of specifications, the lead circuit board welding surface of the extended length of less than 1.5mm. This reduces the workload of preparing and pin trim components , but also better board by soldering equipment.
( 5 ) Avoid using a snap to install a small stand and radiator because it is slow and requires tools. Should try to use the casing, the plastic rivets fast access , use double-sided tape or mechanical solder connection .
7 Conclusion
For use through-hole technology circuit board assembly manufacturers who , DFM is an extremely useful tool , it can save a lot of costs and reduce a lot of trouble . Use DFM method can reduce engineering change and the future make concessions in the design, these benefits are very straightforward.
