IPC Standard Surface Mount Requirements Automatic assembly considerations for surface mounted components are driven by pick-and- place machines used to place/position chip components, discrete chip carriers, small outline packages, and flat packs. Printed board designs shall maintain appropriate clearances for the automatic pick-and-place equipment to position the parts in their proper orientation and allow sufficient clearances for the placement heads.

IPC Standard Surface Mount Requirements Typically, fine pitch devices could be between 250 and 775 mm 2 case size for automatic placement without vision. Generally, the largest component that can be placed with vision alignment is 1300 mm 2, measured to the outside of the leads. Large packages exaggerate the effects of the thermal mismatch between the component and substrate.

IPC Standard Surface Mount Requirements Normally, the minimum size leadless component that can be placed with automatic equipment is 1.5 mm nominal length by 0.75 mm nominal width. Smaller components require high placement accuracy. Vacuum pickup with standard equipment is also difficult.

IPC Standard Surface Mount Requirements Avoid extremely small passive components. Leadless passive components should have an aspect ratio greater than one and less than three. High aspect ratio parts tend to fracture during soldering. Square devices (aspect ratio = 1) are difficult to orient.

IPC Standard Surface Mount Requirements Smaller components are easier to solder, but footprints must be large enough to permit reliable placement of adhesive without smearing onto the conductor. Avoid components which require mounting land spacings (on the same component) closer than 0.75 mm, due to process limitations on applying (chip bonding or thermal adhesive).

IPC Standard Surface Mount Requirements High profile SMT components (higher than 2.5 mm) interfere with wave solder flow to adjacent components, and should be avoided. Special orientation symbols should be incorporated into the design to allow for ease of inspection of the assembled surface mounted part. Techniques may include special symbols, or special land configurations to identify such characteristics as pin 1 of an integrated circuit package.