Product category: Electronics Manufacturing Machinery and Materials
News Release from: Tecan | Subject: Barbed clips
Edited by the Electronicstalk Editorial Team on 13 February 2006
Clips put a new
barb on applying PCB screens
New technology can significantly cut the production time needed to solder large RFI screening cans and fences onto printed circuit boards
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New technology from RFI screening specialist Tecan can significantly cut the production time needed to solder large RFI screening cans and fences onto printed circuit boards (PCBs). OEMs, CEMs and in-house PCB assemblers can now cut production time by employing a novel 'barbed' retaining device which holds the screening can wall in position during the reflow process.
During reflow soldering the PCB can warp, not necessarily a problem for small components, but this does cause problems for devices such as multiple-cavity screening cans and screening walls with long edges where solder joint gaps and inconsistencies can occur.
To overcome this problem customised clamps are often used to secure the screening can to the board during the reflow process.
Typically these are cumbersome, time consuming and expensive.
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Screening cans suit automatic assembly
Standard RFI screening cans can be supplied on pick-and-place tape reels for the convenience of small, medium and high-volume OEMs and CEMs
Another way is to solder the screening cans separately by hand, which is also time consuming and labour intensive.
The new barbed retaining tag technology negates the need for any of these processes and, in a recent application where the customer was hand soldering, saved 80% in production time.
The new technology involves a barbed retaining tag which is an extension of the screening can wall itself.
The tag protrudes through an oblong hole in the PCB and holds the wall / can securely in position at several points along its length.
The PCB can then be confidently reflowed with the can in position, resulting in a post-reflow assembly with consistently good solder joints.
The system also has advantages over recent 'clip' methods, where several separate retaining clips are strategically reflowed to the PCB - so that the screening can/fence can be simply push fitted into position later.
A disadvantage with this system is the need to recess the can edge at the points where they correspond to the clips (to ensure RFI integrity via close contact with the PCB).
The clips are also susceptible to breakage if the can is removed from the board for rework access.
Warping and bowing problems typically occur with screening cans over 75 x 75mm.
The new barbed retaining tag technology is ideal for all needs beyond this and particularly for multiple-cavity and labyrinth screening components.
The company has now established calculation criteria, based on individual PCB thickness and size, which allows it to ensure optimum success for any given size of board.
They then advise on the exact size of the retaining slot size, and sequential location points, to ensure coplanar retention of the can/fence to ensure successful and consistent reflow during the oven process.
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