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Issues depaneling

Kevin

#13429

Issues depaneling | 23 November, 1998

A buddy of mine has problems after depaneling double sided pre-scored PCB's. Resistors near the edge, after put into the slice and dice machine contain micro cracks. He's checked for them before and after depaneling. We figure it is the sectioning or the depaneling. Has anyone come across this before?

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Keith

#13430

Re: Issues depaneling | 24 November, 1998

| A buddy of mine has problems after depaneling double sided pre-scored PCB's. Resistors near the edge, after put into the slice and dice machine contain micro cracks. He's checked for them before and after depaneling. We figure it is the sectioning or the depaneling. Has anyone come across this before? | Yes you are right. The stresses involved in depanelling scored pcbs is underestimated and can crack chip components. Our answer was to stop scoring pcbs and resort to routing circuits for depanelling by a different machine cutting the webs joining circuits to the frame. | |

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Michael Allen

#13431

Re: Issues depaneling | 24 November, 1998

What kind of "slice and dice machine" do you use? I assume you're referring to what I call a score-breaker -- a device to separate the board from the panel (or from the adjacent board) by crushing the score-line WITHOUT bending the panel or the board(s).

I would be surprised if this kind of device puts any significant stress on the board or the components. I would ask if someone is breaking the scores by hand (i.e., without using the machine).

If you find that this type of machine really is damaging the components, please let me know!

| A buddy of mine has problems after depaneling double sided pre-scored PCB's. Resistors near the edge, after put into the slice and dice machine contain micro cracks. He's checked for them before and after depaneling. We figure it is the sectioning or the depaneling. Has anyone come across this before? | | |

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Scott Snider

#13432

Re: Issues depaneling | 25 November, 1998

| A buddy of mine has problems after depaneling double sided pre-scored PCB's. Resistors near the edge, after put into the slice and dice machine contain micro cracks. He's checked for them before and after depaneling. We figure it is the sectioning or the depaneling. Has anyone come across this before? | | | We have used a pizza cutter for one year and have had several false alarms concerning cracked components. In 90% of the cases it turns out someone took a shortcut and broke the panels out by hand instead of using the cutter. We solved this problem by increasing the material remaining after the score to .025". With this amount of material remaining it is VERY difficult to break the board out by hand. Now the pizza cutter is used 100% of the time. The other 10% problems were associated with components spaced too closely to the edge of the board (per the equipment manufacturers recommendations). We solved these problems by moving the components or changing the dielectric to a sturdier one. Check out the Kemets white paper "Ceramic Chip Capacitors "Flex Cracks" Understanding & Solutions" by Jim Bergenthal.

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Michael Allen

#13433

Re: Issues depaneling | 25 November, 1998

A word of caution: thick webs (i.e., shallow score grooves) can result in scrapped boards, especially if you've got the dual-wheel-type score breaking machine.

I discovered recently that shallow score grooves, combined with DULL knife-edge guides on the score breaker, can allow the boards to jump "off track". When this happens, a dual-wheel-type score breaker will quickly slice the board in two.

To avoid this, sharpen the knife-edge guides frequently AND/OR specify a deeper groove (i.e., thinner "web").

I should mention that, like Scott, I have been specifying a "web" dimension of 0.025" for 0.062" boards. This web is relatively thick according to our board supplier AND according to the supplier of our score-breaker machine; I guess most shops specify about a 0.020" web (or less). But I want to deter hand-breaking of scores, AND to reduce the chance of accidental breaking of scores during upstream processes.

I think our short term solution will be to keep the web dimension at 0.025" and simply sharpen our knife-edge guides more frequently.

Our long term solution might be to replace our dual-wheel score breaker with a competing model that uses a sliding parting wheel on top and a stationary, linear blade (guide) on the bottom. This single-wheel-type score breaker does not require the board to slide against the knife-edge; instead, the board is stationary and the parting wheel slides over the board. I'm guessing (?) that this method produces less scrap because it's less sensitive to both dulling of the bottom blade and shallow score grooves. In addition, it won't jump "off-track" when the parting wheel encounters a hole or a routed-area (which is another problem with the dual-parting-wheel machines).

| We have used a pizza cutter for one year and have had several false alarms concerning cracked components. In 90% of the cases it turns out someone took a shortcut and broke the panels out by hand instead of using the cutter. We solved this problem by increasing the material remaining after the score to .025". With this amount of material remaining it is VERY difficult to break the board out by hand. Now the pizza cutter is used 100% of the time. | The other 10% problems were associated with components spaced too closely to the edge of the board (per the equipment manufacturers recommendations). We solved these problems by moving the components or changing the dielectric to a sturdier one. | Check out the Kemets white paper "Ceramic Chip Capacitors "Flex Cracks" Understanding & Solutions" by Jim Bergenthal. | |

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