Jim Hisert’s Tech Support Blog

Electrostatic Discharge

We all need to be aware of the dangers that face electronic components.  Electrostatic discharge can cause a component to fail immediately, or shorten the component's life by damaging it.  I found an interesting article (click here to read about an unusual ESD accident) about a mine worker who was actually hurt by electrostatic discharge.  Although you and I have little to worry about bodily injury from ESD on the production line, it’ll probably come to mind next time you wear ESD boot straps or a carbon-lined jacket.

Other Benefits of a Good Solder Joint

Proper solder joints provide mechanical, electrical, and thermal interconnections that are reliable over the course of a product’s lifespan.  Unreliable interconnections not only cause product failure, but extend the products time-to-market, cause recall/redesign issues, and increase the amount of rework and line maintenance necessary to keep up with product demand.

Successfully forming a solder joint in most situations is easy, although demanding applications often call for unique alloys, difficult surface finishes, and non-recommended reflow windows.  If you are struggling with these types of issues, searching the internet may not be the fastest way to find a solution.  Send us a question at www.askus@indium.com or call (315) 853-4900 for a much more custom fit answer to your one-of-a-kind problem.  

Say Hello to the New Halogen-Free No-Clean Ball Attach Flux

Following the success of NC-506 (No-Clean flux for mounting spheres on BGA packages) is a halogen-free version – NC-585.  I’ve been working with this flux quite a bit lately to see how it stacks up with the industry leading NC-506.

The first thing I noticed was the lower tack and viscosity of NC-585.  This was apparent in initial pin-transfer testing.  The flux rolls well under the squeegee blade and transfers a large amount of flux per pin.  Because the transfer is so pronounced, NC-585 may bridge between very closely spaced pins, we will need to take a closer look at this later.  Normal BGA pitches are no problem at all with this flux.

The wetting of this material was surprising.  I didn’t think any halogen-free flux would be able to compete with NC-506, but NC-585 had even better wetting characteristics on bare copper and ENIG surfaces at Pb-free temperatures with SAC 387.

The future of this flux looks promising, as does the future of powerful halogen-free fluxes.

Frustrating Echoes

Every so often I hear my own voice echo back while I’m talking to someone over the phone.  This can be very annoying when dealing with a technical issue.  Does anyone know how to fix or minimize this without disconnecting?

National Semiconductor Realizes Industry Value

In a recent interview, National Semiconductor CEO and Chairman Brian Halla proclaimed what we should all hold dear: “Everything that is important to this world will be solved by semiconductor technology.”  Click here to read the interview.

Solder Paste Dipping for PoP and Rework

What’s the difference between Package-on-Package (PoP) / BGA rework solder paste, and solder paste designed for SMT?  Solder paste for dipping applications is designed to transfer more solder based on its rheological characteristics.  In the chart shown here, a typical SMT paste is compared to 3 next generation dipping pastes.  Although the names cannot be released right now, all PoP/rework pastes transferred over 100% more paste to the solder joint area.  (Hint: you can probably break me down relatively easily if you have me on the phone.  For the whole story call me at (315) 853-4900)

This added solder volume helps ensure that more solder is available during joint formation to compensate for component warpage.  During rework, increased solder volume replaces solder that has been scavenged during the component removal process.  Either way, more solder volume relates to a more robust solder joint.

Semiconductor Packaging Materials - Find What You’re Looking For

• Are you looking for information on semiconductor packaging materials?  Send your request to jhisert@indium.com.  It’s all fair game – released, experimental, or competitor materials.  Flux characteristics, paste properties, application methods…

   

  Inquire about any of the following topics:

  • Pin transfer
  • Package-on-Package (PoP)
  • Solder spheres
  • Glass transition temperatures (Tg)
  • Flip chip assembly
  • BGA rework
  • Cross-sectioning electronic components
  • Paste for component dipping
  • Solder alloys
  • Liquid fluxes
  • Wafer bumping
  • Low alpha solder
  • Spin coating
  • Redistribution layers (rdl)
  • Halogen-free
  • Flux viscosity
  • Solder paste viscosity
  • Whatever else you are interested in

Pb-free Thermocouple Fix

A set of wires prepared for connection

Properly joined thermocouple wires

Thermocouples do a lot for us.  We use them for profiling reflow ovens, checking material temperatures, and a host of other temperature related measurements.  They see a lot of abuse and they are bound to break with enough rough use.  So how do we fix broken thermocouple wires?  I have a method that works very well.  It may not be the cheapest way to fix the wires but it has the following advantages:

• Pb-free joint
• Highest thermal conductivity of any current method
• Good for use up to 280°C
• Strongest connection (40,000psi tensile strength)
• Requires no specialized equipment

This method can also be used to convert leaded thermocouple wires to pb-free.

Here’s how:

1) Clip the ends of the thermocouple wires so they are even

2) Strip the sheathing back as shown in the picture (1/4inch)

3) Use a razor blade or emery paper to scrape the oxide layer off the wires, then twist the ends together

4) Put a very thin (~.001”) layer of NC 506 flux on the surface of a ceramic coupon and the exposed thermocouple wires

5) Place an 80Au/20Sn preform or a sphere(s) of the correct volume on the flux layer

6) Place the coupon onto a hotplate set to 400°C

7) Bring the wires over to the Au/Sn (which should now be molten)

8) Dip the wires into the solder

9) The solder should wick onto the wires, when it does – remove the wires.

You can leave the no-clean flux residue on the wires, or wipe it off using a solvent and rag.  You now have a high-temp pb-free thermocouple.

If you'd like to discuss this with me, click here or just give me a call @ (315) 853-4900 x-7592. 

A Package-on-Package “How To”

A new tutorial on assembling package-on-package components is available.  Click here for the PoP Guide and other application notes.

Surface Tension Affects Capillary Underfills

After discussing flux removal (which is usually a precursor to underfilling) it is only natural to discuss capillary underfilling.  Low bump standoffs cause problems with water soluble cleaning, and similarly make capillary underfills difficult to use under standard conditions.  Some capillary underfill manufacturers may have alternative materials for the tightest applications, so double-check that you are using the best possible material.  Even though it may be tempting to crank up the underside or nozzle heat, stick to the underfills specified ranges.  You can check the flow characteristics of an underfilled flip chip by CSAM or dye-n-pry methods.  Poor underfill flow will result in air pockets around the solder bumps after cure.