1. The Pick & Place Process
During the SMT component placement process, components are picked from tape etc generally by means of a vacuum pickup, They are then automatically aligned and oriented by the machine before placing in position on the pre pasted PCB.
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2. Pick & Place Applications
The primary function of standard pick and place systems is to populate PCB's with components prior to reflow. However a number of special applications are being required of the systems as technology advances, these include semiconductor applications such as die placement, package on package etc aswell as placement of membrane switch assemblies. To enable these applications, engineers are having to design very specific feeder options thus increasing the potential uses for the equipment.
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3. Pick & Place Machine Types
All SMT placement machines operate on the same principle of vaccum/suction pickup of components from reels or trays etc, alignment and placement.
However there are a large number of different techniques employed for the component alignment and in the placement heads.
Basic systems usually employ a mechanical centering technique which physically aligns the component against a mechanical datum, this method is not recommended for more advanced packages due to potential damage and lack of accuracy.
Non contact laser centering is employed in mid range systems. This technique involves rotating the component within a laser beam enabling the system to determine orientation. This is a much better system and produces very good accuracy.
High end systems make use of full vision alignment using a camera and vision system to ensure accuracy of placement. The component is aligned on the fly as it passes over the camera field of view. This method as well as being the fastest way of aligning also gives the benefit of being able to check component legs and BGA balls for presence and damage, prior to placing and rejecting if appropriate.
Although entry and mid range pick and place systems use a single nozzle pickup head, the higher end systems employ multi nozzle heads for speed of placement. Various turret and cam systems have been employed to accomodate the number of nozzles/heads used, and systems with up to 30 nozzles are commonplace.
Entry and mid range systems are often stand alone whilst the more advanced systems are all inline for volume SMT manufacture.
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4. Troubleshooting Pick & Place Problems
Pick and place performance is largely down to the programming, calibration and optimistation of the placement machine. However certain problems can cause reflow issues and poor quality yields. Here are a few things to look out for:
Cracked Components..
Although this phenomenun is usually associated with mechanical centering methods causing damage, it can also be caused by poor support tooling and excessive placement force..
Mispicks..
Mispicks are common issue with regard to pick and place machines and are usually caused by poor maintenance (nozzle and feeder cleaning), bad feeder/pick position setup, bad components and faulty/broken nozzles.
Component movement/off position..
Components that seem to be placed in the wrong position either prior or after reflow can be results of a number of things.
Melf components that are glued have a tendency to move due to the high body of the component pushing the positioning off in the glue.
Poor tooling setup can cause erratic placement aswell as component damage.
Calibration and offset issues often also result in misplacement.
However a correctly calibrated and setup pick and place machine will offer very reliable performance.
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5. Expert Advice..
Please visit individual supplier websites for further detailed information.Browse manufacturers pick and place machines here
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