Professor Michael Dickey: Prophet of Gallium Liquid Metals

North Carolina State’s Professor Michael Dickey is arguably the world expert on applications of liquid gallium metal. See his Tedx Talk and also his recent Jones Seminar at my university, Dartmouth College. Professor Dickey has found many interesting applications that may be future products. Some of the applications are, for lack of a better word, clever.

Look at these two videos and see if you agree.

Most interesting is his emphasis on the “softness” of liquid metals and how this feature will enable liquid metals to be the foundation for wearable electronics. As a company that provides high-quality jettable liquid metal and liquid metal paste technology, Indium Corporation is very interested in his work and the new applications of liquid metal. 


Dr. Ron

Optimizing Test Cost Webinar

There are many cost drivers in today’s electronics manufacturing environment. That is why it is important to eliminate unnecessary cost wherever possible.

In a new free webinar, Optimizing Test Cost, EDM’s test engineering team discusses how best to optimize inspection and test strategy. Product design considerations, automation, standardization and best mix of test technologies are discussed. Test robot options will also be demonstrated. The webinar length is 20 min with a 5-minute Q&A.

Date: Tuesday, November 2, 2022

Time: 11 am Eastern Time

To register, click here.

Join Me at SMTA PanPac 2023


I’ve gone to SMTA PanPac since 2018 and it is a terrific conference. This coming year’s conference, from January 30 to February 2, 2023, will be another great experience. The venue is striking as seen in the photo. Admittedly, it is small, but that is one of its attractions. In addition, the people that go tend to be leaders in the field. Since it is small, you will get to know everyone there.

So please submit an abstract and please come.


Dr. Ron

Square vs. Circular Apertures and the Five Ball Rule Revisited


I recently posted that circular apertures deliver much less solder paste than square apertures. One of the obvious reasons is that a circle of diameter D has only 78.5% of the area of a square of side D. However, in addition, the circular aperture has poorer release than a square aperture. In the aforementioned post, I theorized that the reason for the poorer release is that the curved surface of the circular aperture adheres to the solder paste solder balls more effectively.

I recently thought of the above situation in light of the “Five Ball Rule.” This rule states that the solder paste’s largest solder particle diameter should be such that at least five of these particle diameters would span the width of a rectangular stencil aperture.

See Figure 1 for the Five Ball Rule applied to circular and square apertures. Note that the ratio of solder balls is 19/25 = 76%, almost the theoretical maximum ratio. However, for square and circular apertures, the ‘Eight Ball Rule” is suggested. But, in some configurations the Eight Ball Rule may result in less solder paste — 40/60 = 62.5% (Figure 2). It should be remembered that this is just a surface area argument, not a volume argument. Solder paste is printed in volume and in this discussion we are just looking at one layer of paste.

Figure 1. Circular apertures provide only 76% of the solder paste that square apertures do using the Five Ball Rule.
Figure 2.  Circular apertures provide only 62.5% of the solder paste that square apertures do using the Eight Ball Rule.

However, the bottom line is that square apertures should be preferred over circular apertures.


Dr. Ron

Grounded! What The Electronics Industry Can Learn from Airlines

Anyone who has boarded a plane in the past several months knows this all too well: the near-term future of airlines is up in the air.

From smallest to largest, all the carriers have been dramatically affected by the post-Covid rebound in passenger air travel. Delta and United Airlines each cut 30% of their respective staff in 2020.

And while many observers point to the attractive buyouts the carriers dangled before critical employees (read: pilots) as means to cut costs amid the mass groundings during the pandemic, employment has shot up over the past 18 months.

Take Delta, for instance. The second-largest airline in the world has hired 18,000 new employees since January 2021. But even with its staffing back to 95% of what it was pre-Covid, capacity reportedly is some 10 percentage points lower. Reason: it takes time to train the newbies.

“The chief issue we’re working through is not hiring but a training and experience bubble,” said Ed Bastian, CEO, Delta.

And the more complicated the job, the longer the training period. Which reveals yet another crack in the fuselage: a lack of trainers. To wit: American says its pilots are basically stuck waiting for training classes to open up, as the number of new hires far outpaces the available slots. The backlog is said to be six months or more.

The issue runs so deep, it has its own name: the Juniority problem.

United has gone on the offensive, blaming — who else? — the government. United chief operating officer Jon Roitman estimates “over 50% of our delay minutes and 75% of our cancels in the past four months were because of FAA traffic management initiatives.”

But all this comes back to the industry’s lack of foresight — or unwillingness — to continue to invest in its workers during the inevitable economic cycles.

You know where I’m going with this.

The PCB industry is historically boom/bust. We are coming off a run of very strong years, and the forecast, according to Dr. Hayao Nakahara, the preeminent researcher in the industry, continues to look bright.

But the graying of the industry is very real, and its long past time OEMs invested in recruiting and training the next generation of designers, design engineers and manufacturing engineers. (And yes, I am pointing at OEMs, since they are top the of the pyramid and ultimately their needs are the driver for the rest of the supply chain’s decision-making.

Let’s learn from the airlines, or, more precisely, their mistakes. It’s time for the push to onboard the next generation of engineers to take flight.

Conductor Sizing Software: How Much is Knowledge Worth?

My name is Mike Jouppi and I am the sole owner of a software application for sizing electrical traces in Printed Circuit Boards.  A description of the application is here.  

I would like to sell this software application and all of the material that went into creating it.  My company has developed 68 design charts.  It also has the capability to create charts for any technology and tools to import the results into the software application.

The electronics design community has started to recognize the importance of the pre-design phase of conductor sizing.  Altium has incorporated IPC-2152 for trace sizing and has training on the topic.  There are many calculators on the Web that are applying IPC-2152 design charts.

Unfortunately, very few understand the physics behind what they are employing as a tool and continue to add confusion to the electronics design community.

If you are interested in contacting me for a conversation on this topic and having a discussion about purchasing my company’s software, my email and phone number are provided below.

Mike Jouppi

Thermal Management LLC


Excel Software Tool to Determine Mass Fractions in Binary Alloy


Recently, I posted a derivation of the equations to determine the mass fractions of two metals in a binary alloy. I thought it may be helpful to develop an Excel software tool to perform these calculations.

To use the tool, you enter the densities of the two metals and the density of the alloy in the blue cells as seen in Figure 1 below. The calculated mass fraction of each metal is shown in the gray cells.

Figure 1. The data entry for the mass fraction calculator. The densities are entered into the blue cells and the mass fractions are calculated and shown in the gray cells. 

As an example, let’s assume you purchase some 14 karat gold. Unfortunately, to your eye it looks more like 10 karat gold, so you want to check it out. As a reminder, when gold is expressed in karats, the alloying metal is copper. First you need to measure the density of the gold alloy. An easy way to do this is the wet gold technique as discussed in a past blog post. From using this technique, you determine that the density of the alloy is 11.53 g/cc. The density of gold is 19.3 g/cc and that of copper is 8.96 g/cc. You will recall that 14 karat gold is (14/24) gold or a mass fraction of 0.5833.

The weight fraction of gold is shown to be 0.4167 or 10/24, as shown in Figure 1, indicating that the gold is 10 karat, not 14 karat.

Time to complain to the seller!


Dr. Ron

How to Calculate the Metal Mass Fractions in a Two-Metal Alloy System


I was surprised to see the wrong formula for metal alloy density calculations on YouTube. The wrong (Eq. 1) and correct (Eq. 2) formulas are shown in Figure 1. In many cases, Equation 1 will give an answer only a few percent off. However, in some cases it can be off by more than a factor of 1,000 as seen in a past blog post. This blog post also gives the derivation of Equation 2.

Figure 1. The wrong and right equations to calculate alloy density.

The YouTube video mentioned above did suggest one interesting task—determining the metal mass fractions of a two-metal alloy, while only knowing the alloy density. Of course, we know the densities of the two metals. The solution to this problem is seen in Figure 2.

Figure 2. Solving for the mass factions of two metals in a two-metal alloy. 

To check the result, assume we have a tin-lead metal alloy. The alloy density is 8.4 g/cc. Tin has a density of 7.29 g/cc and lead 11.34 g/cc. By plugging these numbers into the solution for x (tin), we get 63% and y = 37%. Hence, this alloy is the tin-eutectic alloy.

This technique can solve only two-metal alloy system mass fractions.


Dr. Ron

New Excel Software Tools to Practice for SMTA Certification #2: Reflow Profiling


In my last post, I shared about an Excelbased software tool called Line Balancer to help candidates for SMTA Certification prepare for the line balancing part of the program. They can use Line Balancer to check the correctness of practice line balancing problems. This post will discuss another Excel-based software tool, Reflow Profiler, to help candidates prep for the reflow profiling part of the certification.

Typically, the reflow profiling goal is to determine if the reflow profile matches the requirements of the solder paste specification.

As an example, let’s consider a reflow profile as shown in Figure 1. The solder paste specification is shown in Figure 2. We will first solve the problem by hand and then use the software.

Figure 1. A ramp-to-peak reflow profile.
Figure 2. The solder paste reflow specification

The first task is to determine if the ramp-to-peak rate matches the solder paste specification outlined in red in the specification shown in Figure 3. By measuring the change in temperature in Figure 4 from point A to B and dividing it by the change in time from those points, we see in Figure 4 that the ramp-to peak-rate is 0.857°C/sec., and is within the recommended specifications 0.5 to 1.0°C/sec.

Figure 3. The solder paste specification with the ramp-to-peak rate highlighted.
Figure 4. The reflow profile with the ramp-to-peak rate calculated.

Figure 5 shows the solder paste specification with the time above liquidus (TAL) with the peak temperature highlighted. While Figure 6 shows the reflow profile, where the TAL is measured as 60 seconds and the peak temperature at 240°C, both are consistent with the recommended values.

Figure 5. The solder paste specification with the TAL and peak temperature highlighted.
Figure 6. The reflow profile with the TAL and peak temperature identified.

Lastly, Figure 7 shows the solder paste specification with the cooling ramp rate highlighted and Figure 8 shows the reflow profile with the cooling rate calculated as -2.8°C/s, again within the specification.

Figure 7. The solder paste specification with the cooling rate highlighted.
Figure 8. The reflow profile with the cooling rate calculated.
Figure 9 shows all of the calculations performed and matched to the specification with Reflow Profiler.

If you are interested in a copy of Reflow Profiler send me an email at [email protected]

Dr. Ron

New Excel Software Tools to Practice for SMTA Certification #1: Line Balancing

I recently developed some Excel-based software to help those who are planning to take the SMTA certification exam to practice. 

In this post, I will discuss the tool that performs line balancing. In a typical SMT assembly line, the placement machines are the “gate” in the cycle time of the line. To assure that their cycle time is the lowest, the placement machines must be time balanced. For example, suppose a simple SMT assembly line has one chip shooter and one flexible placer. Let’s say that the chip shooter takes longer to place all of the chips than the flexible placer takes to assemble the simple and complex integrated circuits. So, in this case, chips should be removed from the chip shooter and be placed on the flexible placer. But how many should be moved to the flexible placer? Determining the number requires algebra, and to understand how to do it, we need a numeric example.

Let’s do an example. In an assembly line, the “gate” in the cycle time is component placement.

  • The chipshooter (CS) places passives at 60,000/hr and Simple ICs (SICs) at 4,000/hr
  • The flexible placer (FP) places complex ICs (CICs) at 3,000/hr and SICs and passives at 8,000/hr
  • The bill of material (BOM) is 354 passives, 12 SICs, and 4 CICs
  • If the FP takes less time to place the CICs and SICs than the CS takes to place all of the passives, then move some of the passives to the FP to time balance the line
  • Let’s check the situation that the FP takes: (4 CICs / 3,000/hr) + (12 SICs / 8,000/hr) = 0.001333 + 0.0015 = 0.002833hrs
  • The CS takes: 354/60,000/hr = 0.0059hrs
  • So, move chips to the FP—but how many? Let’s call the number x. The times should be equal, so:
    • 0.002833+x/8000 = (354-x)/60,000.  Solve for x to time balance the line.
    • 0.002833+x/8000 = (354-x)/60,000, multiply each side by 60,000
    • (60,000*0.002833) + (60,000x/8000) = 354 – x
    • 170 + (60/8)x = 354 – x,  gather x terms
    • 170 + ((60/8) +1)x = 354, gather numbers
    • (68/8)x = 354-170 = 184, solve for x
    • x = (8/68)*184 = 21.65 or 22 passive moved to FP

Let’s see if the times on each machine are the same.

  • CTCS= 332 passives/60,000 passives/hr =0.005533 hrs or 19.92 secs

Is the FP the same?

  • CTFP = 0.002833 + 22/8,000 = 0.005583 hrs or 20.10 secs

Why the difference?

The times can’t be exactly the same as we rounded the number of passives moved to the FP.

Figure 1. The “Line Balancer” answer to the problem

Figure 1 shows the calculations from the Excel® software tool I developed called “Line Balancer.”  Note the answers are the same. If you would like a copy, send me an email at [email protected].

Here is a problem for you to solve:

  • The chip shooter (CS) places passives at 50,000/hr and Simple ICs (SICs) at 3,000/hr
  • The flexible placer (FP) places Complex ICs (CICs) at 4,000/hr and SICs and passives at 7,000/hr
  • The bill of material (BOM) is 390 passives, 14 SICs, and 6 CICs

How many components need to be moved, and to which placement machine? What is the cycle time?

To the first person that sends me the answer, I will send them a Dartmouth hat.