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December 2006

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Subject:
From:
John Burke <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, John Burke <[log in to unmask]>
Date:
Tue, 19 Dec 2006 16:17:18 -0800
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Hi Phillip,

I cannot seem to find this thread maybe our server went down - However, you can of course use different thermode materials such as ceramic Thermodes with built in heater/sensor systems, the ideal being good heat conductivity with very low mass so you can heat the solder and cool down to solidus while still under Z axis clamping pressure. I think you may be using a titanium thermode?

Maybe the joints you are making are being "let go: in Z axis before they are set?

And no you don't have to use metal polish to remove residue from the heads, a good solvent will remove the residues. If they prove tough use an abrasive such as a very short horsehair brush (SUB 1/8TH INCH) in conjunction with the solvent to remove the residues and do it frequently.

Also make sure that the head has some degree of freedom to "float" to ensure co planarity, and / or do frequent tests of head to base co planarity using a pressure sensing film (sometimes you do not want the head to float for very fine pitch as it can move the top flex surface causing a bad assembly). When cleaning the heads put a straight edge along the front face of the tool with a light source behind it to make sure that there is no bowing of the tool from end to end, and that there are no "dinged" areas which can cause poor soldering

Hope this helps


Kind regards,
 
 
John Burke
 
(408) 515 4992

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phillip Bavaro
Sent: Tuesday, December 19, 2006 3:40 PM
To: [log in to unmask]
Subject: Re: [TN] Hotbar soldering process controls

At the moment, we are looking at xray of the solder joints as a process control if we can correlate the peel test results from good and bad connections to the xray image.

  The manufacturer recommended method of removing residue from the head was to use an abrasive metal polish.  This naturally gives me nightmares so I will need to find a better method of cleaning the residues off.

  The connection in this situation is basically a plated through hole bonding two metal layers with polyimide layers in the middle.  This seems very unreliable as the only two stable locations are the PTH and the castellation at the end of the flex circuit (near the end of the pad).

  Does anyone know of any published guidelines for flex circuitry design that I might be able to find out more about this type of soldering connection?

  Thanks in advance,

  Phil


Werner Engelmaier <[log in to unmask]> wrote:
  Hi Phil,
Depending on design, the commercially available soldering bars remain
sufficiently flat up to about 2 inches in length [for more details, see my papers
Engelmaier, W., “Transverse Joulean Heated Soldering Tool for Mass Terminations,”
Proc. NEPCON/West, Anaheim, CA, February 1979, pp. 228-235.; and Engelmaier,
W., “Transverse Joulean Heated Double-Sided Reflow Soldering Machine for Mass
Terminations,” Proc. NEPCON/West, Anaheim, CA, February 1981, pp. 333-339].
Actually more of a concern may be temperature uniformity, which becomes even
more of a concern with lead-free solders.
One other concern is the amout of solder present—too much and you get shorts,
too litlle, well...One solution is a soldering bar with a bottom surface that
is not flat, but rounded, thus giving you solder joints that get thicker away
from the bar center and thus being able to successfully accommodate a larger
variation in solder volume.

Werner

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