BTU Tritan Solar Cell Furnace

Ovens used in the metallization of solar cells can have 20 or more heating and cooling zones.  These ovens can become quite long if the conveyor speed in the initial curing and final cooling sections are the same as the firing section.  By speeding up the conveyor speed in the firing section the oven can be shortened and temperature of the cells can be increased and decreased more quickly.

Multiple conveyor speeds are also encountered in food processing lines where the food product passes through a several machines running at different speeds.

ECD’s newest profiling software can accommodate multiple conveyor speeds.  Most profiling software assumes the

Solar Cell Metalization Time-Temperature Profile

conveyor speed in all zones is the same.  ECD’s new M.O.L.E. MAP® software version 2.18a allows entry of a different conveyor speed for each zone. 

Proper positioning of oven zones on profile time-temperature data requires accurate knowledge of the conveyor speed.  By knowing the sampling interval, length of each zone and the conveyor speed one can calculate how many temperature samples “long” a particular zone occupies.�

Reach For the Sun

Solar Cell manufacturing has been around for a long time; however the materials and process have changed drastically in the past few years and will continue to evolve as the technology and need for Renewable Energy grows. The costs of manufacturing and the risks associated with the ever changing processes can strain  the ability to maintain yields and improve quality. Proving these new manufacturing processes, then achieving the repeatability and yield needed for production have always been a challenge.

ECD’s suite of profiling tools allow detailed Characterization of these advanced processes  during the R&D phase.  During production ramp-up good thermal thermal profile data drives yield improvement leading to maximum profitability.   In  production these same tools can quickly Verify that the optimum manufacturing  process is being maintained.

Thin Film Solar

ECD has many types of customers in the Solar Cell manufacturing industry.  They include start-ups, university research departments and production facilities, located around the globe. 

The application areas that we have been able to identify are among the following:

Silicon Metallization:
   Thermal profiling is used to optimize the drying, rapid firing and following cooling process in the oven.

Silicon Diffusion:
   Thermal profiling is used to optimize the heating, high temperature diffusion and cooling process in the oven.

Thin film Solar Cells:
Done on glass and other substrates, this process is similar to Diffusion process, but at lower temperature.

Profiling Equipment Requirements:
Minimum profiler thickness is important – Many of the ovens designed for solar manufacturing provide little vertical clearance for the profilers.   Thermal barrier requirements vary and in some cases, time and temperature do not allow pass-thru profiling.  In most cases 3 channels of thermal data are sufficient for process verification as all areas of the silicon heat similarly.   Thermocouple attachment can also be tedious, with mechanical pressure being the most common contact method.

We look forward to the continued growth and success of the Solar industry and we would like to invite all solar industry participants to work with us and discover how we can help you reach your performance goals.

Good solder joints are not enough.  A good reflow profile must consider component temperature limitations.

The new IPC standard released Dec 08, Classification of Non-IC Electronic Components for Assembly Processes, J-STD-075, calls for thermal classification of components, and recommends a marking system to help contract manufactures recognize component temperature limits during the soldering process.  Failures don’t show up during initial test, but much later on in the product’s life – often six months to two years later, and well below forecasts that drive pricing and warranty policies. ALL parts have temperature limits; and until we take the time to profile the process to which we subject these parts, we can’t know if we cause harm or not.

ECD has moved in that direction with our Thermal Quality Management (ThQM™) Program. We think this will give the industry the knowledge and tools to look at ALL components in the comprehensive light necessary. Equally important, it introduces a program and method of dialog between OEM and EMS provider on soldering process issues.

View full details here

There is more than one way to specify thermocouple size.

Thermocouples are made when two conductors (wires) of different metals (alloys) are connected together to form a “junction.”  This junction, or connection between the two conductors, is typically made by melting the two conductors together using a torch or a flash welding process. The size of the thermocouple is typically specified by the size of the two conductors, however, rather then the size of the junction formed where the conductors are melted together. The junction size is typically 2.5 time the wire diameter or less.  Since the junction can vary somewhat, it is not the best way to specify the thermocouple size. So we us the wire size. Below are several of the most common ways to specify the size of a thermocouple:

• Gauge (American Wire Gauge, or AWG)
  Wire gauge is common in the US and has meaning in the electronic and electrical fields. It’s handy because it keeps you from having to say (or write) long decimal numbers like 0.005 inches in diameter when you can just say 36 gauge. However, it’s upside-down in that as gauge number goes up, wire diameter goes down. There is a ratio between the gauge size and the diameter in inches:

Wire Diameter (inches) = 0.005 * (92^((36-AWG)/39))

As messy as this is, we still use AWG to call out thermocouple wire size. Here is a table of some common wire gauge sizes and their diameters in inches:

AWG            Diameter (inches)
22                   0.0253
24                   0.0201
26                   0.0159
28                   0.0126
30                   0.0100
32                   0.008
34                   0.0063
36                   0.005
38                   0.004
40                   0.0031

• Wire diameter
  We also size  thermocouple wire by the diameter of the conductors. Each of the two conductors will be the same diameter, of course. See the above table for typical conductor conductor diameters use in the US.
  
• Square Millimeters (mm²)
  Most other countries in the world use what’s called cross sectional area to specify the wire size. This is nothing more then the area of the circle formed by the conductor if you were to look flat at the end of the conductor. You know the area of a circle is:

Area =∏*radius²

And since the rest of the world is metric, this area is in millimeters (mm²). Common wire sizes are in nice round mm² numbers which means common sizes do not match up well with the AWG sizes.  The table below shows the mm² sizes for the AWG gauge sizes:
AWG                mm²
22                   0.326
24                   0.205
26                   0.129
28                   0.081
30                   0.051
32                   0.032
34                   0.020
36                   0.013
38                   0.008
40                   0.005

The most common thermocouple wire gauge sizes used for reflow or wave  soldering in the US are: 30 and 36 AWG, and some 40 AWG
A common size in other countries is 0.03 mm², which as you can see from the table above is neither 30 nor 36, but real close to 32 AWG. The method used to specify a thermocouple size really depends on where (what country) you are buying it from. Although we can all convert, and most make equivalent sizes, what you will hear on the street will be AWG size in the US and area in millimeters most anywhere else in the world.

Box-whisker plots are a great way to show how stable the different thermocouple attachment methods are relative to each other.

The top dot is the Maximum value and the bottom dot is the Minimum value from the data set. The top of the box is the 75th Percentile (AKA: 3rd Quartile) and the bottom of the box is the 25th Percentile (AKA: 1st Quartile). This makes the Median, the red dot, the 50th Percentile (AKA: 2nd Quartile). Percentile is a number describing the data set such that the K-th Percentile is a number such that K % of all data values are less and (100 – K) % are larger than it, or to be more precise, at least K% of the sorted values are less than or equal to it and at least (100 – K) % of the values are greater than or equal to it.

Aluminum foil promotes solid contact with surfaces – Kapton tape adds adhesion insurance

What are some advantages of Aluminum Foil Framed in Kapton Tape?

Easy to remove without damage to product
Stable – good long term
Allows use of smaller pieces of foil while maintaining adhesion

What are some of the disadvantages of Aluminum Foil Framed in Kapton Tape.

Two step operation requires more time

The Sticky T/C is easy to attach and remove multiple times

What are some advantages of Sticky T/C?

Quick and easy to attach and remove

Does not damage product
Can be attached to metals and plastics
Provides identification of instrument input channel number
Able to see through and accurately place thermocouple

What are some of the disadvantages of Sticky T/C.

Not usable with small or irregular surfaces such as component leads

Product Information Here

The Temprobe is the easiest to use and remove attachment method

What are some advantages of Temprobe?

Quick and easy to attach and remove

Works well on “wet” solder paste

Does not damage product
Can be attached to metals and plastics
Sheathed construction protects thermocouple

What are some of the disadvantages of Temprobe.

Requires 1/2- 3/4  inch virtical clearence above board in oven

Air Dry Epoxy provides solid contact but requires time to cure

What are some advantages of Epoxy?

Stable – good long term
Can be attached to metals and plastics

Easy to see

What are some of the disadvantages of Epoxy.

Proper cure may require hours
Difficult to remove without damaging product
Difficult to recover thermocouple

Aluminum foil promotes solid contact with surfaces

What are some advantages of Aluminum Foil?

Easy to apply
Easy to remove without damage to product
Stable – good long term
Accurate – Can be attached to very small components

What are some of the disadvantages of Aluminum Foil.

Does not work well with very small contact areas such as component leads
Cannot see through it to know where thermocouple is placed