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August 2012

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From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Thu, 16 Aug 2012 09:53:34 -0500
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In a couple of companies I work for, we fabricated and installed a small heated ultrasonic flux sprayer on the Mydata or Juki pick and place machines. The pick head is programmed to pick small flip chips and CSPs and move them over the sprayer, which is then toggled for the time duration controlled by the machine programming. The sprayer is inside of a shroud to keep the flux from traveling through the air inside the PP cabinet. It works pretty well, but needs to be cleaned at the end of each shift. However, different fluxes don't always work the same way for a given spray setting, but for long-term high volume it works very well, and can be controlled to provide just enough of a coat of tacky flux on the bottom of the chip. The heater control is the toughest part, as the tacky flux is "eutectic" in nature, by that I mean it turns into a liquid when heated to 100 degrees Fahrenheit, and back into a gel within a few minutes at room temperature. Conventional liquid benchtop fluxes do not work very well, as the solids tended to clog up the spray head.

-----Original Message-----
From: Amol Kane (Asteelflash,US) [mailto:[log in to unmask]] 
Sent: Thursday, August 16, 2012 9:04 AM
To: Stadem, Richard D.; TechNet E-Mail Forum
Subject: RE: CSP BGAs

Hello Richard,
So you are talking flux only attachment?......I carefully added flux with a manual dispenser and a fine gauge syringe after printing and placement on some test vehicles and the BGA did solder (brushing flux BEFORE printing does not help as the paste deposit does not stick to the pads). However we will be building hundreds of these assemblies and I need a repeatable process. There was flux voiding based on the amount of flux each part got. 

I just wanted to validate my hypothesis about the HIP and graping on such tiny components and see if anybody was already using dip fluxers for such components

Thanks!
Amol


-----Original Message-----
From: Stadem, Richard D. [mailto:[log in to unmask]]
Sent: Thursday, August 16, 2012 9:51 AM
To: TechNet E-Mail Forum; Amol Kane (Asteelflash,US)
Subject: RE: CSP BGAs

Simply brush a very thin layer of a good tacky flux such as Alpha WS1208 over the pads prior to placement. Even a very thin layer of this flux will be more than enough to allow good wetting to the pads.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Amol Kane
(Asteelflash,US)
Sent: Thursday, August 16, 2012 8:34 AM
To: [log in to unmask]
Subject: [TN] CSP BGAs

Dear Technetters,

We are going to be assembling some lead-free  1.6x0.8 mm micro BGAs with 0.5mm pitch and 0.17mm dia board pads. Anybody else have experience with this small a package?....I am concerned that there won't be sufficient flux in the tiny solder deposit to clean the oxides during reflow, leading to graping and/or head in pillow situation. Do I need a dip fluxer for the part to do a flux only attachment, or to augment the amount of flux in the solderpaste-solder bump system? I am told I have no time to do DOEs to determine stencil and reflow parameters, so I am turning to technet for help.....any thoughts?

 

 

Regards,

Amol

 


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