How to Do PCB Assembly DFM?

PCB assembly DFM analysis refers to the PCBA processing company to help customers to do the manufacturing analysis before production on the line. PCBA processing manufacturers based on years of experience in processing, targeted analysis of PCB circuit board structure, proposed improvements to optimize the layout of lines and components, making the products fabrication more in line with the manufacturing process, improving products quality and stability.

1\PCB Size

PCB dimensions need to meet the following requirements:

when the PCB size is less than 50mm×50mm, it must be designed as panel and then the size of panel less than 420×350mm.

PCB four corners recommend to use the rounded corners.

2\ PCB Process Edge Requirements

• From the edge of the PCB 5mm is not recommended within the layout  of component pad, MARK
• Conductive copper foil should be as wide as possible
• Irregular PCB must be crafted edge, if it doesn't have panel design
• Hand Plug components of the entity can not fall on the upper and lower process edge within 3mm width of the space,and can not fall on the left and right side of the process edge 2mm width within the space

3\PCB Silkscreen Requirements

• All components,mounting holes and heat sinks have corresponding silkscreen labels and bit nubmers
• Polar components of the polarity of the direction of identification to be unified, easy to identify, component placement should not cover the polarity logo. In particular, Digital identification is easy to identify
• The Identification of the device on the PCB must be exactly the same as the identifier in the BOM list
• Silkscreen can not be on the pad,and its labs should not overlap, cross and should not be placed after the mask bock, to avoid the hole caused by silkscreen incomplete

4\PCB Basic MARK Requirements

The whole board mark should be placed on the TOP and BOTTOM surface

The whole board has at least three marks, which are L-shaped

It is not allowed to have pads, vias, test points or silkscreen logo and so on wihin mark pointsΦ3.0mm.Mark point can not be cut by V-cut machine,because it can not be indentified

Mark center distance from the PCB board at least 5mm

Mark requires a clean surface, smooth, smooth edges, neat, color and the surrounding background color is significantly differnt.

5\SMD Layout Requirements

• For the hot air reflow process, the placement of components for welding have a certain impact. Components should be placed in the direction of wiring, assembly, welding and maintenance requirements, as far as possible uniform. Elements on the PCB requires a unified direction,and the positive and negative elements should have a unified direciton
• SMD layout prohibited area: from the PCB long edge 5mm and short side 3mm range should not have the placement of components, if you need to install components,which can increase the edge of the process
• Components layout direction requirements: The orientation of the Chip components should be perpendicular to the direction of Soldering;The orientation of the IC components should be parallel to the direction of Soldering
• Red plastic reflow curable curing process components requirements: red plastic curing only play a fixed role in the components, so it needs to choose a samll package components, such as: CHIP(0603,0805,2520),SOT23,SOT143,SOT223,SOIC.The red plastic curing can be used in the following components package:exclusion,BGA,SOJ,PLCC,CSP,SOT89/SC-62,SOT252,SOT263/SOT268 and so on
• For QFP,SOP,SOJ and other IC pads, pad pins can not be directly connected.It should be connected in the outer area. Lead line can not be drawn from the middle of the pad and should be drawn from both ends of the pad.
• Reflow soldering element components at both ends of the pad of the thermal symmetry requirements: In order to avoid the device after the reflow soldering bias, monument phenomenon, reflow soldering element components at both ends of the pad should ensure thermal symmetry, pad and wire The width of the connection should be greater than 0.3mm
• large area copper foil and pad connection requirements: the use of heat insulation tape SMD device with a large area of copper foil thermal isolation, can reduce the tombstoning, Weld, poor solder joints and so on
• Jumper Wire do not pur under the IC or motor, potentiometer and other large metal shell under the components
• If there are Φ12 or more 12mm with square hole on the PCB, which  must make a hole cover to prevent solder outflow
• Over-wave soldering device plug-in spacing is greater than 1.0mm, in order to ensure that when the wave soldering is not even tin, over wave soldering components plug edge spacing should be greater than 1.0mm

6\Wave Soldering Tray Tooling Design Requirements

• Wave soldering tray tooling is designed for BOTTOM surface patch componets of PCB.
• The height of the bottom patch is not higher than 3mm(except in special circumstance)
• Try to use the chip package, reducing the number of tray openings
• The long side of the opening of the tray as much as possible with the PCB on the line in the same direction of movement

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