Seth J Homer

Power amplifiers and transistors come in many shapes and sizes. The performance requirements vary as well. Attaching them can be a critical aspect of your design.

Both Pb and Pb-free alloys can be manufactured as a solder preform with a flux coating.(Learn more)  Selecting the right alloy and flux coating can be crucial to meeting your void criteria.  

A high-tech SOLDERING solution might include NanoFoil®, which effects a solder joint while minimizing heat exposure to your components.

There are also thermal interface materials such as the HEAT-SPRING® which utilize the unique properties of indium to create a superior thermal connection, similar to a solder joint.

There are many different attachment methods available, contact me with your design parameters and we can find your solution.  

Considering a fusible alloy as a solution really starts with the applications temperature profile. When cooking a turkey (pop-up timer) or supressing a fire (sprinkler systems), its all about the heat and what the fusible alloy does in response to it.  Reliability is achieved through ensuring that each alloy is homogenious and not subjected to segregation. Take a look at our list of alloys, and you'll find that there are many options to choose from, many of which are Bismuth containing. These can be manufactured in many shapes and sizes and due to the high volume nature of these applications, the need for tape and reel is almost a given.
 

The binary eutectic alloy of bismuth and tin (Bi/Sn) is well suited for many low temperature applications due to its melting point of 138°C, but the alloy is known for being rather brittle for a solder alloy.
All hope is not lost though - there is a similar alloy, known as Indalloy 282, which drastically reduces the brittle nature of the Bi/Sn alloy with the addition of just 1% Silver (Ag).  This 57%Bi/42%Sn/1%Ag alloy has a 1°C higher melting point.  Although you won’t be able to notice this reflow change, you will immediately notice the physical difference if you compare solder wire made from each alloy.  The Bi/Sn wire is likely to break upon bending, unlike the Bi/Sn/Ag alloy.
The easiest (and most economical) way to experiment with these alloys is with a solder wire kit . With a wire kit you can obtain both wires in the same diameter, and you get 5 fluxes to help with soldering.  You can also get up to 10 different alloys if you want to experiment-your-heart-out and compare Bi/Sn and Bi/Sn/Ag to other alloys like Sn/Pb or Sn/Ag/Cu.

I can't promise that every gold-indium or copper-indium soldering process can work without a flux, but there are tricks to give you a better chance of obtaining the flux-less thermal assembly that eludes so many thermal engineers. The indium itself won't build up a thick layer of oxides (see Amanda Hartnett's blog "Indium Oxide Layer"), so the problem is generally the substrate oxides.

Some people have used an emery cloth followed by an alcohol rinse for Cu oxide removal, which should work.  The surface preparation that is used in labs is different though.  I prefer to use 15% - 20% Nitric Acid or 5% - 15% Sulfuric Acid to clean copper for 2 – 5 minutes.  Other acids are also used – it is just important that the acid is strong enough to remove the oxides, and can be fully cleaned after etching is complete.

While the acid etch process can be used to remove initial oxides, it does nothing to protect the surface from oxygen attack during reflow.  This requires flux or forming gas.  The reducing chemical reaction between hydrogen based forming gas and oxides starts to occur at or above 275degC.  Below that temperature, the gas works as an inert atmosphere.  The Au and Cu parts may be cleaned very well by exposing them to this gas at a high temperature, and introducing clean indium at a lower temperature (using the gas as an inert atmosphere).  Superheating the indium to +275degC is not advised though, since excess intermetallics may result. 

The hydrogen will not be a true reducing atmosphere at typical indium reflow temperatures.  Although the forming gas does nothing for indium, it will at least be of use with the Au and Cu metallizations.  The inert properties of the gas will definitely help protect the assembly from oxygen at soldering temperatures.

Tape and Reel

Tape and Reel has been on my mind a lot lately. Staying on top of this preform packaging trend is important.

Whether we're looking for the right size pocket, cover tape, or even the orientation of the part, the name of the game is always performance. If the peel force isn't within a tight spec or the pocket is too large, then a drop in pick performance is imminent. Everyday there is a new challenge and new part someone wants placed in tape. Just when we think we've seen it all, a customer will come to us for help on something new.

Were always looking for new challenges, so feel free to contact me with yours.  

This question was posed to me while introducing a family member to the world of Engineered Solders this past weekend. While I was still reeling from the shock of what seemed like a ridiculous question, it suddenly occurred to me that solder is not part of everyone's daily life. Actually it is, they just don't know it. Take a moment to run through the average day. Before you get through the morning you have probably taken solder for granted more often than you realize.
Usually the day begins with the dreaded alarm clock we all wake up to (Solder Paste) and the flat screen HDTV we watch the morning news on(Thermal Products). Need I mention the cell phone (Engineered Solders)?

Indium has over 200 alloys to choose from.(Alloy List) The list is always growing, but the diversity in solder types is exceeded only by the applications in the industry.
With close to 75 years of contribution to the ever changing world of solder, Indium has been a leader in technology and education. Right down to the correct spelling of the word.