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SMD Removal using ChipQuik alloys
By Ahmad Tabbouch - Created Friday, November 12th 2010 @ 23:59:04 ADST

Today we'll be looking at ChipQuik Inc's low-temperature rework alloy (known simply as "ChipQuik"), a god-send for SMD removal/repair both on and off the field!

ChipQuik sampler pack containing 2.5ft of alloy, tacky flux and alcohol swabs

ChipQuik is essentially an alloy containing Bismuth as its main constituent, which in-itself has an inherently low melting point. Once the alloy is heated and combined with standard Tin/Lead or Lead-Free solder, the overall melting point drops dramatically to just under 60oC (as opposed to the typical 180~200oC for tin-lead)

This in-turn means the solder will remain molten (or at least, malleable) for a longer period of time, allowing you to perform extensive repairs to both through-hole and SMD boards without the need for specialised equipment. It also minimises the possibility of damaging the PCB substrate, solder mask, pads or surrounding components due to heat-related stress

Removing an IC without affecting surrounding components

For the sake of simplicity, we'll be removing a small 20-pin SSOP package (an AC'97 codec) from an old XBOX mainboard. The same process can easily be used on larger components with a higher pin density (ie: TQFP144) after you've had some practice.

Here is our target:

Board with AC'97 codec to-be-removed

We'll be using the following tools and consumables:

  • Soldering station: Preferrably temperature-controlled
  • ChipQuik Alloy: SMD4.5 NL or SMD1 NL
  • Paste Flux: AMTECH NC559-ASM / RMA-223, or ChipQuik's SMD291 sampler squeeze-tubes
  • Kapton Polyimide Film: 10MM or 25MM width
  • Antistatic Tweezers: Straight or Angled depending on preference
  • Solder Wick: Goot 3MM braid, again depending on preference
  • Cannabis: One quart of hydro, available on your nearest dodgy arab

We're now ready to begin! Due to the extremely low melting point of the alloy, it may be a good idea to turn down your 'irons heat setting (thank to Grant of UltraLogic For the tip!)

Masking out the surrounding components
Use Kapton Tape to protect the surrounding components, only leaving the IC exposed
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Masking out the surrounding components
The surrounding components are now fully masked
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Fluxing the compnent leads
Apply a generous amount of paste flux across all the component leads
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Applying the alloy
Melt the alloy and counter-intuitively drag it across all the component leads
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The alloy, now applied
All pins now have the alloy applied (seems like an techs nightmare at first!)
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Reflowing the alloy
Now we re-heat both sides until the alloy re-flows
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Grasping the IC
Grab the IC with your tweezers, and twist it slightly
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Grasping the IC
Gently lift the IC off the board
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Removing the IC
Remove any remaining alloy with solder wick
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Completed board
Tape removed revealing clean pads, ready for the replacement component

Easy as that! You can obtain ChipQuik alloys, tape and fluxes through the following Aussie retailers:


Doug Ford Analog Design
Mektronics
Jaycar Electronics
Diverse Technologies

-PodeCoet
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