No Clean Solder Paste

Maria Durham, Indium’s new Technical Specialist in Semiconductor and Advanced Assembly Materials, has been doing some research on indium lead (In/Pb) solder alloys. We chatted about her findings this week. 

 [Andy C. Mackie: ACM] Which indium/lead solder alloys are most common, and what are their properties?

[Maria Durham: MD] Firstly, the use of lead-(Pb-)containing solders in some soldering applications is restricted due to local environmental and RoHS compliance, but there are still many applications where they are  allowed. Many military, aerospace, and industrial equipment uses, as well as many applications related to vehicles, are exempt. The table below shows the most common indium/lead (In/Pb) alloys (pink) and their properties, sorted by liquidus temperature; the higher of the two melting points (solidus and liquidus) seen for non-eutectic alloys. In blue are three comparison materials.

Indalloy 205 is the most commonly used, probably because it has the closest liquidus temperature to the tin/lead eutectic (183°C), 63Sn/37Pb (Indalloy 106). This means it can be reflowed using a standard Sn/Pb eutectic profile. The next most common alloys that are used are Indalloy7, 204, and 206.  Besides the melting range, indium has comparable thermal and electrical conductivity to standard materials.

[ACM] What makes indium-lead (In/Pb) solders so attractive, and why have we seen a recent resurgence in their usage?

 [MD] One main attraction to using indium/lead (In/Pb) solder alloys in soldering to precious metal surfaces is that, unlike tin-containing solders, they do not leach gold. That is, gold does not dissolve in them to any appreciable extent. During discussions at Semicon West in 2011, one of our California customers reported going through 8 simulated reflows with Indalloy 205 in contact with a gold surface with no loss of joint strength and no joint embrittlement. That is pretty impressive. Note that embrittlement is often caused by gold-intermetallic formation. It has been noted that even at 250°C, 50In/50Pb dissolves Au at a rate 13 times slower than it does into 63Sn/37Pb, although this, of course, is a kinetic, not a solubility limit, study.

The higher melting Indalloy 164 (92.5Pb/5In/2.5Ag) has the lowest coefficient of thermal expansion (CTE) of all of the In/Pb solders and is able to withstand the higher temperature excursions that can be seen in step-soldering type applications (where a very high melting solder is used to form the first joint, followed by a next lowest melting alloy, and so on). This is seen in applications such as power electronics assembly, where the first step solder is often used for die-attach either as a solder paste, wire, or preform. The high melting point helps the solder withstand the operational temperatures associated with under-the-hood electronics, in applications such as engine control modules, where Indalloy 151 (92.5Pb/5Sn/2.5Ag) or Indalloy 163 (95.5Pb/2Sn/2.5Ag) are most commonly used. In/Pb solder is excellent on very rigid structures such as ceramic-to-metal or ceramic-to-ceramic. The desired solidus / liquidus temperature range can be adjusted by changing the indium:lead ratio, making it very easy to “dial in” the alloy to a specific reflow process.

Another attraction to using In/Pb solders is that they exhibit good fatigue resistance in thermal cycling from -55°C to 125°C.  In testing, the 50In50Pb solder joint fatigue life is about 100 times greater than that for 63Sn/37Pb.

 [ACM] What fluxes are used in these applications, and how are they formulated differently?

 [MD] The fluxes most compatible with the lower melting point (<200°C) indium-containing solders are NC-SMQ-80 (solder paste) or the lower-tack TacFlux® 012 (suitable for use with wire, preforms, and spheres). These are no-clean fluxes, specifically formulated for lower temperature reflow.  Under appropriate low temperature reflow these fluxes leave behind benign residues that do not need to be cleaned off (“no-clean” flux), although they are often cleaned off in most practical applications, usually to ensure reliable wirebonds absent of flux spatter.

 To learn more, please contact us.

 Cheers!  Andy

We are frequently asked if it is possible to solder to aluminum. The answer is yes, if the following guidelines are followed: 

FLUXES:
Because it is difficult to solder to aluminum, Indium Corporation developed Indalloy Flux #3 (activation temperature is 96-343°C) to remove the tenacious oxides that prevent the solder from wetting to the surface. This flux is very corrosive and is not recommended for electronic applications because, if any of the post-reflow flux residue remains after a warm water rinse with mechanical scrubbing, the joint may be compromised. This flux is recommended for mechanical assembly joining applications only. 

Another alternate solution is to use a forming gas consisting of nitrogen and hydrogen. This method of oxide removal is generally used when the soldering temperature is greater than 350°C which is ideal for activating the hydrogen to reduce the oxides. With this method, there is no post-reflow flux residue to clean up.

METALLIZATIONS:
An alternate to corrosive fluxes is to nickel plate the aluminum so a weaker flux (RA, ROL1) can be used. These fluxes are less corrosive and can be easily removed with an appropriate solvent.   There are many solder alloys that will wet to nickel. Check out our solder alloy physical properties table.

SOLDER ALLOYS:
The solders that are normally recommended for joining aluminum are:

• Indalloy #201 (91Sn, 9Zn); 199°C E
• Indalloy #176 (95Zn, 5Al); 382°C E. 

Here is a question that was posted and answered on our website back in 2006, I think it is still quite relevant:

Question: “Why does your Application Note for cleaning of indium ribbon for thermal interface recommend a mild (5-10%) HCl acid solution, yet [the] MSDS for Indalloy #4 (100%) says to avoid contact with acid? My past indirect experience with indium usage indicated some cleaning procedure of the oxides was necessary to achieve good thermal contact resistance.”

Answer: “Thanks for contacting the Indium Corporation with your request. If the indium ribbon is stored and handled (stored unopened in an argon or nitrogen pack – placed in a dry box) properly and it solders well in your process, this procedure should not be necessary. When following this procedure, the HCl solution should be applied to the indium metal to clean it thoroughly, and then dried with nitrogen.”

If you want to know more about metal thermal interface materials (TIMs) (handling, preparation, or process parameters), send an email to our global technical team at: askus@indium.com. They are ready to answer your question!

~Jim

Tombstoning

• the transition to Pb-Free (higher reflow temperatures, and related flux issues)
• miniaturization (0201s and 01005s)

• The reflow oven operator can slow down the ramp rate. A slower ramp rate allows for more uniform warming of the PCBA.
• Another technique is to employ a "soak" just below the melting temperature (solidus) of the alloy. For example, for a SAC305 profile (217°C solidus), one may implement a "soak" at 205 to 210°C for 30 to 120 seconds. This allows for the cooler parts of the PCBA to "catch up" to the warmer parts. After thermal equilibrium has been achieved, one can spike the temperature up to the appropriate peak temperature (i.e. 245°C). This technique (depicted in the reflow profile shown at the right) allows for all of the solder paste deposits to melt and wet the component terminations at roughly the same time; thereby, mitigating tombstoning.

Phone: +1.315.853.4900
E-mail: ebastow@indium.com

• exhibit reduced viscosity
• spatter during reflow
• produce excessive oxidation of the solder joint

At the time of writing, the price of silver (Ag) was approaching the USD$50/tr.oz. (Troy ounce) level, and threatening to go higher. With 1 Troy ounce being 31.1grams, this makes the cost of pure silver ingot close to USD$1.60/gram.

Image from goldsilveroz.com

Materials costs are therefore a major consideration for anyone using silver in any form. Naturally, we are now seeing a few Power Semiconductor packaging houses evaluating the possibility of moving away from silver-filled epoxies for die-attach. The alternatives they are considering include the adoption of solder paste (or solder in some other form: wire / ribbon / preforms) versus a silver-filled epoxy.

Here are some thoughts on the Power Semiconductor assembly pros and cons, based on using solder paste as an alternative to silver-filled epoxies.

Good news (+)

+   Reduced materials costs
+   Improved pot-life / shelf-life *
+   Improved high temperature thermal-cycling
+   Strong, metallurgical joint formed between leadframe (substrate) / joining material / die
+   Improved thermal conductivity
+   Faster throughput (more units per hour, UPH)**
+   Easy clean-up ***
+   Does not wick onto NiPd surface to cause poor wire bondability

 * Although it is true that solder pastes are stored under refrigerated conditions, they do not require the -40C storage that is typical of silver-filled epoxies. 

 ** The dispense of solder paste is very rapid and can be done using multi-dot dispense heads. It undergoes rapid temperature reflow, versus the slow cure needed for metal-filled epoxies, which can be up to typically 1-3 hours, depending on the volume of silver epoxy.

 *** Because the solder paste flux does not cure like a polymeric material,  tubing and other conduits for the solder paste are easily cleaned out using common solvents, or can be simply purged with flux.


  ==================

Bad news (-)

-   Capital costs #
-   Adoption time / new process learning ##
-   Needs a solderable die surface
-   Voiding increase ####

 # The main cost-drivers here are:

- Reflow: Specialty reflow equipment is required for high temperature solders, such as
Heller or BTU reflow ovens

- Cleaning: If wirebonding is required after the reflow process, standard cleaning equipment and cleaning chemistry (aqueous or solvent-based) will be needed to remove flux residues

- Gas: Forming gas (H2/N2) or simple nitrogen may be needed to assist reflow.

Note that increasingly, for clip-bonding (non-wirebonding) applications using the new ultralow residue solder paste Indium9.32, even cleaning may not be needed, as the residue has been found to be compatible with compatible with a number of molding compounds in the industry.

 ## By partnering with a company like Indium Corporation with many years of experience in die-attach soldering, the ramp-up time can be significantly reduced.

 ### A solderable surface is usually a sequence of Ti / Ni / (Ag or Au) plated layers. The thickness of the silver (Ag) or gold (Au) precious metal layer is usually limited to 100nm (0.1microns). Compare this to a standard silver-epoxy bond line thickness (BLT) of 0.5-2mils (12-50microns).

 #### Acceptable voiding of less than 5% of the total die area is fairly easily achieved with good quality substrates and die-finishes.

  ==================

In closing, I am indebted to my friend and colleague Sehar Samiappan (Indium Corporation Area Technical Manager - South East Asia) for his insights.

Contact me to discuss this further.

Cheers!   Andy

Conformal coating compatibility with no-clean flux residues has been a major topic for years – becoming even more popular recently with companies looking to cut manufacturing costs and processes.

Unfortunately, no industry standards definitively determine or define “compatibility” between conformal coating materials and no-clean flux residues. This does not mean that people are always automatically cleaning the flux residues before conformal coating their boards. Nor does it mean that most people are shooting in the dark with their decision to clean or not. I have a number of customers who conformally coat over no-clean flux residues, smart customers who have taken the time to do their due diligence and create their own standards and test methods to determine compatibility. These companies also run the tests and apply their standards on their materials.

Here at Indium Corporation we look at materials compatibility from three different viewpoints:

The first is the simplest: visual appearance. Does the coating look like it has adhered to the board, components, and/or flux residue? A lack of adhesion will usually result in bubbles, crazing, and a number of other visual defects or anomalies.

The next step/test that could be taken to determine compatibility would be to measure actual adhesion. “Tape Tests” are often used to measure adhesion. However, these Tape Tests all have a number of imperfections and variables that accumulate to result in a lack of both accuracy and repeatability. For example, many of these Tape Tests are very operator dependent and rely upon the speed at which the tape is removed, the angle at which it is removed, the force in which it is removed, etc. Different operators can, and do, have very different results. Tape Tests are also dependent on the tape. Variables include: age, shelf life, tack strength, adhesion to certain materials, tape brand, tape width and/or length, even test temperature. Another issue with this method has to do with the conformal coating material. What happens when the conformal coating material is a silicone? There isn’t much that will stick to a silicone, so using the Tape Test with this material is probably worthless. Here are several Tape Test procedures that are present within the industry:

• ASTM D 3359-02
• IPC-TM-650 method 2.4.28.1F
• IPC-TM-650 method 2.4.26

Note that the ASTM test method neuters itself by stating all the possible flaws that could be present.

The third viewpoint is electrical reliability using Surface Insulation Resistance (SIR). Even this is not easy to conclusively determine because there are two different test methods for SIR. One each for:

• No-clean fluxes IPC-TM-650 method 2.6.3.3B
• Conformal Coatings IPC-TM-650 method 2.6.3.4A

Another issue with SIR testing involves 3D parts. The National Physical Laboratory (Britain) and the SMART Group (a British trade association) have been trying to conquer these SIR challenges for years. They do have a draft of a standard written, but nobody wants to stick their neck out, without further testing and proof, to release this standard; so it has been in limbo for quite some time. For further reading on this topic, read this paper, authored by my colleague Andy Mackie and me. It provides further insight into the issues that our industry is facing with regard to compatibility. Note the chart, in this paper, that highlights the differences between the two IPC SIR test methods.

Now that you know Indium Corporation’s position on conformal coating compatibility with no-clean flux residues, it is time to consider the point of view of the companies who manufacture and supply conformal coatings. The majority recommend that, when in doubt, clean the no-clean flux residue before conformally coating. This takes any and all of the guessing out of the equation.

As stated earlier, there are companies that conformally coat over no-clean flux residues with success. Some of these companies are very successful and well-known aerospace, automotive, and military organizations. I am sure they have created their own standards and test methods to mitigate risk and doubt, while assuring performance and reliability. Unfortunately, they have not yet shared their methods and/or experiences with the rest of the industry, so we cannot yet use their expertise to guide us as we converge on one industry standard. If you are one such organization, I’d love to hear from you.

We have not done much work with conformal coating “compatibility” trials due to the vast number of conformal coating materials commercially available and the vast number of no-clean flux formulations that we offer. Even if there were a standard that would define what it means to be “compatible”, the sheer number of conformal coating products, when combined with the sheer number of no-clean solder fluxes, creates an extremely large matrix of necessary tests.

In conclusion: When in doubt, clean.

If you have any other questions or concerns please feel free to contact me at any time.

I just visited a customer that was converting from water soluble solder paste to no-clean. Not exactly a slam dunk transition as this customer found out.

During my visit, solder balls and solder beads were observed in the no-clean flux residue adjacent to discrete components (capacitor/resistors). These could potentially be a reliability concern…electrical shorts.

In water soluble processes, solder defects such as solder balling and beading can be washed away in the cleaning process…no worries. However, introducing a no-clean solder paste often requires that the process be “cleaned” up a bit. Here are some ways to do it:

STENCIL DESIGN:
My first step was to investigate the stencil design for these discrete components. Why? Because, since water soluble post-reflow residues (including solder balls & beads) are washed away, many customers will opt to place as much solder (1:1 ratio) as possible on the pads - to achieve a good solder joint. This is especially true for military or medical applications where a robust solder joint fillet is vital. However, because no-clean residues are typically not cleaned, the solder balls and solder beads remain in the flux residue and may produce electrical shorts.

When printing in a 1:1 ratio, especially if the stencil is thicker than average, solder paste is often pushed under the component and onto the solder mask during component placement. Upon reflow, the sub-component solder paste may not pull back into the solder joint. This is one way that solder balls/solder beads are produced.

No one wants to hear that they need to buy new stencils with reduced apertures, but I did recommend, in this case, that some aperture reduction be considered (generally down to 0402 components). Usually a 10-15% reduction, with home-plate or similar design, is common. Many stencil manufacturers are fully aware of the issue and can make suggestions on aperture designs.

REFLOW PROFILE:
Simultaneously, the reflow profile often needs to be adjusted. In the preheat portion of the typical reflow profile, the first few oven zones are used to drive off flux volatiles, making the paste less "mobile". A balance in the ramp rate is vital; too fast - and small “explosions” may cause paste to spatter into other areas; too slow - and two bad things happen: the flux will spread excessively and the flux activity can be exhausted.

Good Starting Points:

• Ramp rate (IMPORTANT: not max slope, see "Best Practices Reflow Profiling for Lead-Free SMT Assembly" for reference): 1°C/s
• Initial first zone setting: 100-110°C

I mentioned in a previous a blog posting that the primary driver for halogen-free electronics is ostensibly environmental, but that the confusion about “which halogens and which molecules and what level?” has seemingly decoupled the laudable desire for an improved environment from the reality and made it more of a marketing tool. All this notwithstanding, there remain some instances where the performance of the final product itself can be directly impacted by the presence of halogens, usually as ionic halides. This is the reason why Indium Corporation recently developed what appears, at first glance, to be an odd combination: a high-Pb (high-lead) alloy halogen-free die-attach solder paste, Indium9.72-HF.

The halogen-related failure mode for die-attach solder pastes is the corrosion of wirebond pads on the topside of Power Semiconductor die which are soldered to the leadframe with halogen-containing solder paste. Many manufacturers producing high volumes of identical power devices may also use die-attach (sometimes called “soft solder die attach”, SSDA) wire to attach the die to the leadframes in a fluxless process, but many manufacturers prefer the inherent flexibility of a solder paste-based process for medium mix / medium volume applications.

Long term blog readers will recall that I did a posting on solderspatter (a.k.a. soldersplatter or soldersplash), and that it can be caused by bubbles of solvent vapor or moisture outgassing from solder paste deposits during reflow. In bursting, the tiny flux droplets or solder particles from the surface of the bubble can be propelled quite a distance (several feet). While solder on wirebond pads is clearly a failure from a reliability viewpoint, certain wirebond pad metallizations may also be subject to corrosion from flux. A poorly maintained reflow oven may also drip flux condensate (usually in the exit – cooling – zone), and this too can be a cause of organic materials on wirebond pads.

As long as the bondwire is gold, and wirebond pads are covered in a uniform layer of gold, there is no problem (as long as the flux residue is washed off) since gold is unreactive, even in corrosive environments. Aluminum (Al) or aluminum/silicon (Al/Si) bondpads, however, are potentially reactive. Halogenated materials, such as fluxes and overmolding compounds may react with them to either reduce the wirebond pull strength and/or increase the wirebond junction resistance, leading to localized heating and subsequent thermal-related joint failure. Even covalently-bonded (C-X, where X is a halogen) materials may dissociate at high temperatures: which is how the banned brominated flame retardants work, of course.

The biggest danger of halogenated flux corroding wirebond pads is when:

1/ Completed assemblies (between the reflow process and the cleaning process) are left for a long time before cleaning; particularly if they are exposed to high humidity (high %RH) before cleaning.

2/ The cleaning process is inadequate: either due to poor selection of the cleaning solution, or poor bath maintenance, or inadequate “scrubbing” energy being imparted to the surface to be cleaned, or simply if inadequate time is allowed for cleaning.

Note that even optimizing 1/ and 2/ may still lead to bondpad corrosion.

The Indium9.72-HF paste is available in both type 3 and 4 powder, in the standard high-Pb alloys, Indalloy 151 (92.5Pb/5Sn/2.5Ag) and Indalloy 163 (95.5/2Sn/2.5Ag), and for larger die that need a higher reliability joint, we also offer the Indalloy 164 (92.5Pb/5In/2.5Ag). A Product Datasheet is available for download, of course.

Cheers! Andy

上週在美國的拉斯韋加斯(Las Vegas), IPC舉辦了美國地區行業的盛會APEX.   Indium公司一如既往的在展會中心安排展位，和業界各位舊友新友交流，與大家分享最新的產品和技術，傾聽大家的反饋和聲音。

除此，在人山人海的技術會議交流中心(paper presentation, educational workshop)，Indium公司的五位大將還為大家做了精彩的演講：

• Ning-Cheng Lee, Ph.D, Vice President of Technology 李寧成博士：

²       Lead-Free Flux Technology and Influence on Cleaning.

²       Selection of Dip Transfer Fluxes and Solder Pastes for PoP Assembly.

²       Achieving High Reliability Low-Cost Lead-Free SAC Solder Joints Via Mn or Ce Doping.
 

• Ronald C. Lasky, Ph.D. PE, Senior Technologist

²       Achieving High Reliability for Lead-Free Solder Joints – Materials Consideration

• Mario Scalzo, Senior Technical Support Engineer

²       Addressing the Challenge of Head-in-Pillow Defects in Electronics Assembly.

²       Challenges for Implementing a Halogen-Free Process

• Eric Bastow, Senior Technical Support Engineer

²       Understanding SIR

• Chris Anglin, Applications Development Engineer

²       Stencil Printing Transfer Efficiency of Circular vs. Square Apertures with the Same Solder Paste

 這些文章在Indium的技術網站上面，都可以免費下載。

Cheers!

This blog has been in existence for a little over two years now, and we would like to thank our readers for the feedback and inquiries you have provided. I welcome your comments on what you would like from us. Leave a comment below, or email me at jhisert@indium.com.

And now a look back on past topics of interest:
 

Grid Ink, Silver Ink, Conductive Ink

Bismuth/Tin Tabbing Ribbon, A Low Temperature Pb-Free Alternative

Plated Metallization for C-Si Solar Cells

Increase Packing Density for Evaporation Crucibles

Photon’s 5th PV Tech Show 2010 USA

IPC Solar Standards Update

Solder Shelf Life as Explained by Eric Bastow

Tips to Speed Your Solder and Flux Selection

What's Happening in the Technical Service Department 

A Day in the Life of a Tech Guy

A Clean Laboratory

CIGS for Beginners

3rd Renewable Energy Expo 2009 in New Delhi, India

Solar Products and Representatives

Kleenex®, Google™, FedX®, CIGs?

Indium Solar Products Reunited

Trade Show Visitors Love the Ground Floor

Solar Product Data Sheets

Intersolar 2009 – What Barrier to CIGS Technology?

Concentrator Photovoltaic Systems - Will they reach 50% Efficiency?

Standards for Solar Panel Manufacturing

Solar Panel Certification: “Barrier and Benefit” Reviewed by Eric Bastow

Low Temperature Metallization Paste

What Will Your Interest Be At InterSolar? Meet the Bloggers And Let Us Know.

Share Your Solar Images

SAC vs. Sn/Ag for Solar Soldering

Solder Thickness for PV Interconnect

What is Bus Ribbon?

Standard PV Interconnect Ribbon Sizes

No-Clean Flux

Photovoltaics in EMS Sector

PV Interconnect Products

Eric Bastow - East Coast Technical Support

Mario Scalzo - West Coast Technical Support

Au/Sn Sputtering Targets

SMT Goes Solar

A Trip Down Memory Lane 

More Information About Metallization Paste

A year in the Life of a Solar Blog

CIG Target

23rd European Photovoltaic Solar Energy Conference and Exhibition

TCO choices for CIGS manufacturing 

CIGS Absorber Layer Electroplating

No Slump Metallization Paste

Meet the Bloggers

CIGS - Can sputtering make a breakthrough?

Fluxes for Soldering Tabbing Ribbon

Computer Brain vs. Solar Photovoltaic

Beam it down from space

Selection of the Optimum Lead-Free Solder for Solar Tabbing Ribbon

Record Makes Thin-Film Solar Cell Competitive with Silicon Efficiency

Why Thin-Film Solar Cells are Here to Stay

Hot Rooftops to Flashy Digital Cameras

Synchronize Your Solar Cell

Solar Conversion Efficiencies  

Government Support is the Key

It's Just a Beginning ...

Graping is a phenomenon which appears as un-reflowed solder particles, typically seen on the surface of the solder joint.  



             Cross-section of “graped” solder joint





The graping phenomena has become more common due to some of the following issues:

1. Reduction of the stencil aperture to accommodate smaller and smaller discrete and passive components (i.e. move from 0603”s to 0402”s to 0201’s)
2. The use of finer particle size solder pastes to accommodate fine feature printing (move from Type 3 to Type 4 to now to Type 5)
3. Higher reflow characteristics for Pb-free soldering
4. The use of water-soluble vs. no-clean solder pastes. No-clean chemistries generally protect the solder powder particles and the metallized surfaces from oxidation during the heating process (after the activator package removes existing oxides). (so how does water-soluble fit into this?)

A combination of any of these factors may exhaust the capability of the solder paste flux to remove surface oxides. This depletes the flux and exposes solder paste particles to oxidation, which means the solder particles do not coalesce into the solder joint.

To avoid the graping phenomenon, use the following tips in setting up your reflow profile. The intent here is to decrease the amount of heat the solder paste experiences during the reflow process.

1. A ramp to peak profile is better than a soak profile   
2. Decrease total time in oven by adjusting the belt speed. A ramp rate of 1°C/ second from ambient to peak is recommended
3. Use a lower peak temperature - 235°-240°C
4. Shorten the TAL to 40-60seconds

Patty, Pete, and John prepare to do battle with "The Big O."

Patty and Pete were able to squeeze in 9 holes of golf, though it was really stressful for Patty. Pete was a good golfer, but not in Patty’s league; he typically shot in the low 80s for 18 holes compared to Patty’s 68-72 range.   Today, going into the 9^th hole, Patty was even par and Pete was one under. He was teasing her relentlessly.   The ninth hole was 532 yards long. Patty used all of her recent training and focused as she drove the ball. Her swing speed hit 114 mph and with a 4 mile an hour tailwind, her drive was 291 yards, 30 yards beyond Pete. Her second shot, with a five wood was 12 feet from the pin. Her putt was dead center for an eagle, Pete’s 8 foot birdie putt lipped out of the hole. Whew! She beat Pete by one stroke! Pete was still thrilled that he gave Patty such a close call.

As they left the golf course, Pete said, “John is really working miracles at the factory, given the constraints he is working under. He has developed a disciplined approach to changeovers and uptime, and has eliminated most waste. But the factory really needs to be cleaner and more organized. With all that is on his plate, and no cleaning staff, he will have trouble implementing a 5S. It will be hard to win new customers with the place looking like it does.”

The next morning, as they prepared for the meeting with Oscar Patterson, Patty noticed that John’s color was ashen.

“John, are you alright?” Patty asked.

 “You’ve never been in a meeting with Mr. Patterson. He can be a bit…uh…. difficult,” John stumbled out.

“From what I hear he is a ruthless, brutal dictator,” Pete added.

John did not disagree.

Patty thought it might be best to call back to her site GM to clarify her mission.

The GM told her, “This guy is a blowhard, it would be great if you could review with him your findings and get his buy-in. But, don’t take any grief from him. He forgets that he sold us his company. Now he has a boss, and it is me. I told him you were going to perform an audit and I want him to work with you.”

So Patty, John, and Pete went to Oscar Patterson’s office to review their findings. Patty was immediately intimidated by him. He was a huge man with a ponderous stomach. But the posters in his office were the worst. One read “I’m the Boss, you aren’t.” Another read, “My way or the highway.” Then she saw, “The Golden Rule of Management: Whoever has the gold makes the rules.” The last one she took time to read was especially troubling: “It’s a question of mind over matter: I don’t mind and you don’t matter.”

Patterson spoke first, “Let’s get this over with, I don’t have time to waste on this nonsense. I’m the boss and I’m responsible for profits, so give me your crap and get out of here.”

The Professor always advised Patty that after an audit it is best to present the strengths first and then the problems. However, never call the problems “problems,” call them “opportunities for improvement.”  “I learned this from my colleague Joe Belmonte,” The Professor told her. She had since met Joe at a few trade shows and was impressed by his wealth of experience and in-depth knowledge of assembly processes.

She started by discussing the very good 25% uptime, and the fact that the operators were quite good at changeovers.  Pete had pointed out that the operators told him that John was responsible for both of these successes. The operators liked and respected John, but realized he had a tough job working for Patterson.

As imagined, Patterson warmed up to this compliments. 

“I told ACME management that buying my company was a good deal. We cut costs and I am able to make a profit even though I have losers like John working for me,” Patterson bragged.

Patty was furious at this comment. Pete looked like he was going to jump across the table and take a swipe at the “Big O.” John just sat there looking defeated.

“This isn’t as bad as I thought it would be,” boomed Patterson. “Continue.”

Patty then reviewed the 7 mudas. She had been surprised that the company did quite well in this part of the audit also, undoubtedly attributed to John:

1. Overproduction

2. Unnecessary transportation

3. Inventory

4. Motion

5. Defects

6. Over-Processing

7. Waiting

Hence, Patty’s comments were positive on this topic.

“You'se guys aren’t so bad,” boomed Patterson. “I told you I was good at generating profits, even stuck with a dufus like John here,” he finished.

At that comment, Pete’s faced turned the most crimson Patty had ever seen.

Patty then went on to “Opportunities for Improvement.” She thought she would start with 5S.

“We performed a “5S” audit of your facility. This manufacturing philosophy consists of:

1.       Sorting

2.       Set in Order

3.       Shining

4.       Standardizing

5.       Sustaining the Improvements,” she started.

“As ACME strives to get more customers for our contract manufacturing services, 5S is an important consideration, as many of our current and future customers practice Lean and especially 5S at their facilities,” Patty added.

As she went on she reviewed the lack of order and cleanliness in the facility. She had photos of dried solder paste on the stencil printers, the flux and dust “stalactites”, and several other examples of 5S violations. Patterson’s face soon matched Pete’s in its level of sanguinity. But he said nothing.

Patty then volunteered that she and Pete would work with John and his team to implement a 5S if desired.

Patty could see Patterson was ready to blow, but she felt she must go on. The only topic left was turning off the nitrogen in the wave soldering machine.  As Patty played the wave soldering video, surprisingly, Patterson seemed interested. 

She continued, “We think an opportunity for improvement would be to re-instate the use of nitrogen in the wave soldering process. First pass yields have dropped from 94% to 87%, thus increasing re-work. Or, perhaps, implementing a more robust wave solder flux. I contacted a wave flux vendor and I have some recommendations.”

At this Patterson became even redder in the face, in a rage he grabbed Patty’s laptop and threw it on the floor, instinctively Pete dove for the laptop, spun around and inserted his chest between it and the floor.  Patty had never seen such agility in a 45 year old man.

“You bozos are worse than John the clown here!" he shouted, as he gesticulated toward John. 

Patterson then kicked the trio out of his office. Pete was ready for a fight, but John and Patty, both visibly shaken, held him back.

Patty immediately called Sam, her GM, and told him in detail their findings and what happened at the meeting. She gave a good impression of what John had accomplished in spite of Oscar Patterson.

“Wow! Patty, I’m so sorry. I didn’t expect it would be this bad. I’ll change my schedule and fly there today. This situation will not stand. Why don’t you and Pete take a break and meet me for dinner at Dinardos at 7PM? Bring John with you.”

Patty was glad that she backed up her files last night on SugarSynch, even though it looked like her laptop was fine. 

Colonial Williamsburg was only a 45 minute drive away, and it was just 10AM. Taking Sam’s advice to “take a break,” she and Pete drove away and toured this beautiful living museum. They also had lunch at the Trellis.

Surprisingly, with the Williamsburg respite and all of the walking Pete and Patty did, they were more relaxed and hungry than they thought they would be. 

On the way back to Dinardo’s Patty asked Pete, “How did you save my laptop, I’ve never seen such an agile, athletic move?”

“Twenty-nine years of beach volleyball,” Pete answered.  “I was good enough that I tried out for the Olympics  in ’92. Humbling experience,” he added.

About 10 minutes before they arrived at the restuarant, Patty's mother called with updates on the wedding plans.....only 10 weeks and counting!

John had arrived early at the restaurant and Patty and Pete met him. He looked very nervous. 

“John, how’s it going?” asked Pete.

“It’s hard to be optimistic,” John answered.

On that note Sam walked into the restaurant.

“This must be John Davis, the new GM, having replaced Oscar Patterson,” Sam stated with great cheer.

These words didn’t seem to register with John.

“Congratulations John, well deserved,” Patty and Pete chimed in.

In the few days they were there, Patty and Pete had grown quite close to John.

As the information sank in, tears welled up in John’s eyes.

“Do you think I’m up to the job?” he asked.

“John, you are already doing the job,” Patty answered.

Epilogue:

Sam had felt it best to have the police accompany him to see Oscar Patterson with the news that he was fired. Patterson became so agitated that the police had to threaten to arrest him before he calmed down and was escorted out of the facility.

With John at the helm, the “shop” was not recognizable in 3 weeks, as he implemented a 5S program that he designed with Patty and Pete.

He performed some DOEs to find a wave solder flux that could perform well, without nitrogen, for most of his applications. However, he still used nitrogen for a few boards that had a large thermal mass. All of these, and the many other, decisions he made were data driven.

Have you performed a Lean audit of your facility? Do you regularly practice 5S and look to eliminate the 7 mudas? Are your decisions “data driven” as John’s are?

Cheers,

Dr. Ron

Shelf life of solder is a concern that is raised by customers on a somewhat regular basis.  Solder pastes typically have a well defined shelf life, however the useable life of a solid form of solder may be much longer and harder to define.  This was the topic of one of my first blog entries, although I think Eric Bastow has a better explaination than I did. Here is Eric's explanation:

“One of the issues surrounding solid forms of solder (no incorporated flux) is determining the usable (or “shelf”) life of the solder. Solder manufacturers have to draw a “line in the sand” somewhere to establish a time limit on the duration of their “warrantee” period. For better of for worse, in our document driven world, many electronics manufacturers live and die by the solder manufacturers stated shelf life, and will even petition the solder manufacturer to recertify the solder after the shelf life has expired so that it can continue to be used. Otherwise, it is excluded from further use and discarded.

There are many solder alloys in existence and each alloy “ages” in a unique way. However, the most common issue with aged solder is oxidation. Is there a level of oxidation at which a solder is no longer usable? With normal storage and handling and use of a flux, the author believes that the answer may be “no” based upon the results of an experiment.

60In/40Pb spheres, 300 microns in diameter, were reflowed in air or nitrogen onto ENIG coupons with two different activity level no-clean fluxes; reduced activity ROL0 (passes J-STD-004A SIR un-activated) and ROL1. The spheres were oxidized to four different levels; fresh, 4 days at room conditions, 5 hours at 85C & 85%RH and 3 minutes of violent shaking. The appearance of the “fresh” was shiny; the “4 days at room conditions” and “5 hours at 85C & 85%RH” were very similar in their slightly dull appearance, and the “3 minutes of violent shaking” were noticeably darkened.

The experiment was performed with a reflow profile that had a peak temperature of 231C. After reflow, the diameter of the wetted spot was measured.

Interestingly, the determining factors were the flux type and reflow environment (air or nitrogen). For a given flux and reflow environment, there was no statistical difference in the size of the wetted spot among the different levels of oxidation.“

-Eric

现在业界中常常使用的是免洗锡膏(No Clean Solder Paste)，也就是说松香残留物在回流后不用清洗去，但是前提条件是这些残留物都是绝缘的，才不会引起桥接短路等故障。因此在评估锡膏的时候，有一项很重要的测试，叫做Surface Insulation Resistance (SIR), 我想中文名字应该叫“表面绝缘测试吧”。

SIR测试，主流的有IPC和Bellcore两种测试方法。直到最近的一个小项目，我才知道，原来IPC早就更新了测试方法中的一些测试条件和要求了。

以前的IPC测试方法，要求在第1天末(24 hours)，第3天末(96 hours)，和第7天末(168 hours)去残留物绝缘值读数。现在的读数要求，已经改成从一开始， 每隔20分钟取一次绝缘值读数，一直到第7天末。如果这些读数有任何一个小于10⁸欧姆的，都被视为测试不通过。 详细的新测试条件和要求，可以看IPC网站上面的说明。

其实这个新要求也很有道理的。现在我们打开电脑或是手机等电子设备，都是要求它们马上正常工作的，有谁会等24小时“预热”时间，保证设备中一切器件工作正常后才开始使用呢？ 因此，电子设备中各种元器件和材料能够在开始的0时刻就一切就绪，对保证电子设备的正常运行，至关重要。那么，对我们材料测试的要求更严格了，也是为了更好的保障最终产品的可靠性，和消费者的利益。

Indium 公司的Eric Bastow 是对SIR测试很有研究的技术同事。

Cheers!

Pic:  http://www.practicalcomponents.com/images/SIR.gif  

Today I made my rounds in the office, collecting ideas for you from our tech guys  - ideas to help you speed the alloy and flux selection process.  The team gave me ideas from the start of the design process all the way up to speeding the order process, and all the steps in between.  These are solder basics, but they can help you get your process up on its feet quicker - if you put together a little information up-front:

1) Call a tech guy early, but be prepared by knowing the specifics of your material needs, like powder size, flux type, and any design requirements.

2) If you’re an engineer specializing in component attachment, get yourself involved with the component or board design team. It may mean extra meetings, but it will save many headaches in the long run after you help the team remember the meaning of “design for manufacture”.

3) Define the details of your application, equipment, and process before selecting a material. For instance, knowing the needle size that you will be utilizing in a dispense machine will speed the powder size selection for die-attach solder paste.

4) Be aware of cleaning requirements and your current in-house cleaning equipment and chemicals before choosing a flux or flux vehicle.

5) Understand the operational temperature of your assembly and the maximum processing temperatures of the components. This will make alloy selection much faster.

6) Don’t get hung up at the ordering process – know what size packaging you need. Do you have equipment that only fits a certain size syringe or cartridge?  Knowing this ahead of time will save you a second call to verify while talking with an Account Specialist.

7) For alloy compatibility and metallurgical considerations, be prepared to lets us know the composition and thickness of your surface finish. This will also save a second call, because it is required information in order for us to get you the right alloy and the perfect flux for your application.

8) For solder paste printing recommendations, know the specifications of the stencil you will be using. Aperture size, stencil thickness, and any other dimensions you can provide will help guide which flux vehicle and powder size we will recommend to you.

9) For preform selection, try using thinner preforms. For prototype situations you can stack the thinner preforms to build solder volume, and it is much quicker to order preforms in 1 thickness as opposed to many thicknesses.

10) Understand your process bottlenecks. By letting us know your material needs we can usually suggest a few materials, but perhaps one of those materials can help eliminate a problem that is slowing your process down.

11) Consider your company’s roadmap for the next 5 years. It doesn’t make sense to select a material and need to select a new one only a year later. Save yourself the time involved in a second solder evaluation and know what the future holds regarding safety/environmental concerns. Likewise, understand the roadmap of your supplier, their future materials, and how their current materials will fit your company’s future plans.

Conductive epoxy is a common material choice for bonding components, especially if the assembly process is temperature-sensitive. Tin-based solder paste or preforms with flux are preferred Pb-free bonding materials; however, conductive epoxies arguably provide advantages over these traditional solder assembly materials. 

It has been my experience that these advantages are perceived in the absence of an awareness of the full solder assembly materials product offering. Specialty solders can provide the same advantages as conductive epoxies and then some.   

Some claimed advantages to conductive epoxies include:

·         RoHS-compliance

·         Ease of assembly

·         No-clean

·         Low cure temperatures

Low-temperature solders such as 58Bi42Sn and 52In48Sn are specialty low-temperature solders which have these same properties including processing temperatures below 150ºC. Both of the referenced alloys are Pb-free, can-be used with no-clean fluxes and are assembled using the traditional solder assembly techniques.

It would seem a toss-up between whether to use a conductive epoxy or specialty solder to assemble temperature-sensitive components except that there are additional advantages to a soldered assembly as compared with an epoxy-assembly. These include:

·         Thermal cycling reliability

·         Solder material consistency

·         Reworkability

·         Thermal Conductivity