Solder Preform

最近有越來越多的客戶問到金錫焊接材料。這些客戶中，多數是做航空航天製造的，醫療器械/零件組裝製造的，或是軍用製造的；它們都對成品的可靠性要求十分高(High Reliability).

金錫電子焊接材料(AuSn Soldering Materials)，通常使用共晶合金80%金20%錫，熔點溫度是280⁰C.  這種合金有很強的焊接強度，抗腐蝕，而且熱傳導效能很好(high thermal conductivity).   如果客戶的板子是厚金鍍層，或是要和貴金屬焊接在一起的，又或有分溫度階梯焊接需求的(step soldering)，金錫焊接材料都是很好的選擇。

 金錫焊接材料焊接材料可以做成焊綫(wire)，泊帶(ribbon)，各種形狀和尺寸的焊片(preform)，或是焊錫膏(solder paste)。Indium公司有專門介紹金錫焊接材料的blog，歡迎參閲。

Cheers!

Pic: Indium Corporation

In the surface mount technology (SMT) electronics and semiconductor packaging industries, Indium Corporation has a reputation for offering custom solutions.  In the world of solar cell manufacturing, I hope that same status is obvious.  I feel custom solutions are even MORE important in emerging technology fields like CIGS cell manufacturing.  Being the leading global supplier of indium (the metal), and a supplier of unique solder alloy shape/size/tolerance forms, we are well equipped to offer you evaporation sources that are tailored to your application.  Sure, we can supply round shot, teardrop shot, wire, ingot, preforms, and various other bulk forms of solder to keep your evaporation chamber filled.  Did you know we can also make custom solder castings to fit your particular crucible?  The process is easy, let us know if you are interested!

(Just click here to get started)

Solderspheres or solder spheres, or even solder balls: whatever you call them, Indium Corporation has been making them for years and has rightly acquired the reputation for doing whatever it takes to meet our customers' unique needs.

Unique Alloys:

Hard to find alloys (like multipart alloys; low-melting alloys and even gold/tin (80Au/20Sn)) are our bread and butter. As "Indium Corporation" it should be no surprise that we lead the world in our ability to supply low-melting indium-alloy solder spheres, as well as other forms of these alloys, such as engineered solders or solder pastes.

Unique Quantities:

We don't want you to buy more than you absolutely need. If you just want 100 spheres, we can easily do that: if you want more - we can do that, too. But remember that, because each customer's need is unique, our prices may be higher than our competitors, especially for more standard alloys. Some customers also have unique inventory-control needs, so we work with many customers to ship on-demand by retaining a buffer stock of spheres here at Indium.

Unique Sizes:

Our current dimensional capabilities as of this writing are from 80microns to 0.062inches, or even bigger. Generally, the bigger the sphere - the less spherical it is (within the limits of surface tension and viscosity), and we can't control the laws of physics, so instances where a very large amount of solder is needed, a preform may have better dimensional control. Also, notice that we won't ask that you order in a specific unit of diameter measurement, like the mil or the micron or the millimeter: we're a global company - just tell us what you need.

Unique Packaging:

Often needed for more delicate alloy spheres, we can offer specialty overpacking that eliminates oxides from the atmosphere around the solder spheres, essentially stopping oxidation in its tracks. It's the same technique we use to package our soft solder die-attach (SSDA) wire: a technique that showed that the very reactive wire was still "as new" 3 years later. We also offer spheres in tape & reel packaging (see image) for 24mil, 35mil and 62mil diameter spheres.

Unique Tolerances:

Just as a case in point, a MEMS customer of ours had a need for a low-melting indium-alloy solder sphere with a tolerance of +/-5microns (+/-0.005mm) for a sphere with a 350micron diameter. That demands a tolerance of just over 1% - pretty demanding, but we did it.

Our standard tolerance is +/-1mil (1 thousandth of an inch, or 25.4microns), but as you can see, we have the capability to go to much tighter tolerances using three proprietary manufacturing techniques.

Other Needs:

We are also seeing people asking for doped-alloy spheres; low-alpha emission solder spheres and other things that we could never have dreamed of...

So please just let us know what you need. We'd be happy to help out, and if we can not do what you ask - we'll let you know why.

Cheers!  Andy

I love watching a good basketball game, and one of my favorite local teams is the Syracuse Orangemen. If you go to a Syracuse home game, notice the shot clock – it was made with Indium Corporation solder. There are a lot of places you can see our products in your everyday life. That smart phone in your pocket, the electrical components in your car, the thermal interface in the computer in front of you. That’s one of the things that makes this job rewarding, being part of so many various applications.

In addition to learning about these different applications, we also get a good reference for what assembly trends are developing, and which material technologies are becoming more popular. 

I’ve watched the halogen-free trend explode and fade, as it was adopted by some large OEMs and their contract manufacturers, but has not spread to most other companies. Another trend that is fading away from the spotlight is Pb-free die-attach solder, since the EU has not found a suitable replacement and has pushed back the exemption deadline. 

A long-existing topic that has had recent mention is solder jetting. The trend towards soldering smaller components is not new or surprising, but for smaller components (01005s and 0201s) we have seen a trend towards dispensing instead of jetting – which seems to suit those applications.

For small component printing, transfer efficiency is critical. Outside of solder paste optimization, “nano-stencil” technology is an upcoming technology that may take-off and improve paste release characteristics. Solder paste is being used in some other creative ways too, like low temperature alloy dipping paste for rework operations. Manycompanies are now using or evaluating specialized solder applications to replace components without fully reflowing the rest of the components on the board.

Integrated preforms are finding their way into more and more applications recently as well. These connected preforms are being used to reduce the need for component pallets and selective soldering operations.

All these applications are great ways that our customers are taking soldering technology to the next level, using materials and assembly methods that were not common before. I look forward to learning how you’d like to use solder in your application!

Those of you have been watching this blog for a while will know that I’ve been keeping tabs on the status of the European ELV (End-of-life vehicle) legislation on lead (Pb), mercury (Hg), cadmium (Cd) and hexavalent chromium (Cr^VI). It’s been both galling and heartening at the same time, to find that when I Google “elv legislation”, this (my) blog keeps coming up as one of the top 10 sources on the subject. OK: enough of the bloggy, solipsistic prevarication...

My friend, Geert Willems of IMEC late last week let me know that the EC (European Commission) had given its final decisions on Annex II ("the exceptions"), and pretty much adopted the recommendations of the Öko Institute from their 127 page report of September last year (2009). I have to say my hat is off to Dr. Otmar Deubzer of IZM and Stéphanie Zangl of Öko for the very thorough and logical background to this legislation.

The decisions that affect those of us in the semiconductor (flip-chip) and power semiconductor arena are primarily the ones on lead (Pb) in solders, that were formerly covered by section 8.a/ and 8.b/ of the old, outdated Annex II to Directive 2000/53/EC, and are now covered by this new legislation.

A quick visual summary of the legislation relevant to lead (Pb) in electrical interconnects is given below, and please consult the original document for confirmation, as I may have missed some subtlety of the legalese in my quest for brevity. Also, frankly, subsection 8 (b) led to some Transatlantic confusion over whether finishes on pin connectors and PWB's were covered(?), but I think the below is correct:




Refer to the table below for the timeline for of each subsection/exception:



Note that the last review of exemptions was carried out in 2009, with potential effect by 1/1/2011. This implies that the legislative hammer will potentially fall on each of those usages slated for future review on January 1st two years after the review year. Lead (Pb) for most electronics attach usages of interest to those of us in semiconductor and power semiconductor packaging may therefore be "legislated out" by 1/1/2016.

Basically, the use of Pb-containing solders in solder paste, die-attach paste, die-attach wire, solder preforms, and thermal interface materials (TIMs) in automotive electronics assembly is safe for now, and changes will not be forced on the automotive electronics assembly industry at a time when even current manufacturing practises may be leading to still-unresolved safety incidents.

Cheers!  Andy

Today (March 3rd) I start my 25th year at Indium Corporation.  It seems like just yesterday that the minor league hockey team I was doing PR for folded and I was forced to look for a new job.

I knew after the first week that I had made a huge mistake.  Going from a world of writing and promoting and ticket selling to day after day of science and chemistry and math couldn't be right for me.  But I needed the job so I stuck it out.  For 24 years so far!  I'll bet I am not the only one with that story to tell.
And it turned out that the move was right for me.  Because Indium is a great place to work with great, smart people but also because every day is different from the day before.  I knew nothing about Indium or indium (the metal) before I started here (other than they were one of the hockey team's season ticket holders and our sports intern's mother worked here).  But I have sure learned a lot since that fateful first week.  Especially about indium metal.  Terms like Solder Preform, Burn In, Thermal Interface and Hermetic Sealing have replaced road trip, slap shot and overtime.

Over the next few weeks I will share with you some of the things I have learned during my tenure here at Indium.  I hope you find them as interesting (and hopefully usable) as I do.

Shelf life means different things in different situations.  Post something on the internet and it will last forever.  Leave fresh fruit out on a hot day and it won't make it through the afternoon.

Jim Hisert recently wrote a blog post on Solder Shelf Life where he teams up with Eric Bastow to discuss Solder Shelf Life.  As they state, Solder Paste has a very defined shelf life because of the flux component.  The shelf life of Solder Preforms, on the other hand, is defined by the solder alloy's propensity to form oxides on the surface of the metal.

How do you minimize Solder Shelf Life issues?  There are several ways:

1) Order quantities that are reflective of your usage. It is attractive to get a large-volume price break, but you need to be able to use the product when the time comes.
2) Request that the solder preforms be packaged in quantities that you use them.  Getting a year's worth of preforms in one bottle may be cheaper, but the constant opening of the jar will only cause the remaining parts to oxidize and become unusable. If you consume 120,000 preforms per year, consider having your order shipped 10,000 pieces per month to assure a fresh supply of material.
3) Store preforms in their original, unopened containers, in a nitrogen dry box.
4) Once you have opened the jar, keep the lid on while it is at the work station.  At the end of the day, return the jar to the nitrogen dry box with the lid off so the nitrogen can purge the oxides that may have begun to form.
5) Consider tape & reel packaging.


 

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

I have been asked on numerous occasions to calculate the potential for galvanic corrosion between metals. Most times, when I am approached with this, the concern stems from an application in which the bonding metals will be mated in a corrosive environment, such as a salt solution.

When the potential is to be calculated for two elemental metals bonding, the potential for galvanic corrosion is simple to calculate. Simply look up the anodic potential difference between the two metals under the galvanic series in a general chemistry handbook and if the value is less than 0.15V (the maximum recommended for a salt solution), galvanic corrosion should not be a concern. For normal environments, such as storage in warehouses or non-temperature and humidity controlled environments there should not be more than 0.25 V difference in the Anodic Index. For controlled environments, such that are temperature and humidity controlled, 0.50 V can be tolerated. 

This value is much more difficult to calculate, however if the bonding metals are alloys rather than elemental metals. 

For instance, I cannot easily supply the anodic potential difference between 80Au20Sn and a pure Au plating to prove that it is less that 0.15V. This is because I cannot calculate the anodic potential theoretically for the AuSn alloy. Data is readily available for pure metals, but the potential for individual solder alloys must be determined experimentally because the voltage potential is not linear and as you begin to add a second metal to a pure metal, the rate of voltage change is different between different alloys. 

For this exact situation, I can speak practically however. We have tested gold plated Kovar lids for corrosion that were sealed to semiconductor packages that had a gold seal ring using a preform of AuSn. They were tested for corrosion in a salt spray chamber per MIL STD 883. Corrosion, when it occurred, always was on the lid where the porous gold allowed underlying nickel corrosion. There was never an instance of corrosion at the Au/Sn and Au interface region.

After a quick survey of a few of the technical service personnel in the office today, I put together a little snapshot of what is happening right now:

Amanda Hartnett and Ed Briggs are conferencing with an engineer that Amanda met at a local SMTA meeting.  This potential customer asked for product recommendations to improve their assembly process after they heard about Indium 8.9HF (a halogen free solder paste).

 


Brandon Judd is working on reducing voiding via profile modification with our flux coated preforms.

Mario Scalzo is tracking and organizing our technical team’s submissions to the Silver Quill program, where authors at Indium Corporation are recognized for technical papers and presentations.

Eric Bastow is helping a customer determine the best soldering materials for a medical application which involves soldering nitinol to nitinol. Common choices are using flux #2 or flux #3 with Indalloy 121 or Indalloy 182 – depending on the application.

And you’re reading what I’m doing right now. One interesting thing that I realized today is how we are working on very different things at the same time, both reactively and proactively. While some of us are fixing customer issues, others are helping to plan future processes to eliminate the need for a fix. 

Something that may not be apparent from this daily description is how this technical team works together. One of the nice things about being in the same office is that we can share ideas and learn from the experiences of our peers.  Even an office mate's tech call or brainstorm session can be a learning exercise. Working together gets us ready for your next call, so we can have the answer for you before it is even asked.

All the best
~Jim H

预成型焊片，Solder Preform，是焊接材料中的一种。最近，Indium公司的美国技术经理Paul Socha的技术文章”Solder Preform Basics” （预成型焊片基础知识）, 在SMT杂志上刊登了。 很快在Indium公司的技术文章下载专区里，也可以下载到。

焊片，通常可以给锡膏印刷的过程起到加锡的作用。除此之外， 如果某些大的元器件焊接需要定量的锡膏，或是通孔(through-hole)的元器件脚的焊接需要比较多的锡膏，焊片都能够定位定量的提供焊接材料。

焊片的外面，还可以含一层薄薄的助焊剂，flux-coated preform.  助焊剂的含量通常在3%或以下，能够有效帮助清除焊接表面的氧化物。

预成型焊片，在北美很多的军事/医疗/航空航天等精密元器件的焊接，都有广泛应用。 Indium公司能够提供各种尺寸，形状，和金，或是包装的solder preforms, 我们的技术团队，更是一直致力于为大家解决焊接/工艺问题，提供最佳的方案。

Cheers! 

Pic: Indium Corporation

 
PS: 很幸运，生活中此后的新篇章我都将和小帆一起写：上个月感恩节，我们订婚了。
 

Eutectic Gold Tin (AuSn) with a composition of 80Au20Sn is a unique material.  This particular alloy of gold tin (AuSn) is considered a solder because it has a melting temperature of 280ºC, which is lower than the 350ºC transition temperature into braze materials.  Still, there are some similarities between this solder alloy and braze alloys. The most obvious is the hardness of the gold tin (AuSn) alloy. With a tensile strength of 40,000PSI, this solder is much more rigid than the tin solders most are familiar with. The strength is more closely compared to the silver brazes which melt above 500ºC. 

With that strength has come some unique manufacturing difficulties. For many years, one obstacle for implementation of gold tin (AuSn) as a solder preform or wire, was its availability in thin forms or fine diameters. The gold tin (AuSn) is extremely hard and it became brittle as it was handled through manufacturing and would crack if it was pressed too thin or fine.  

Luckily, in the 40+ years since eutectic gold tin (AuSn) was first used in electronics manufacturing, processing techniques have come a long way.  Today, gold tin (AuSn) solder can be made into dimensions much smaller than the soft solders, allowing it to be used in applications which require the highest level of precision.

Typical dimensions and tolerances of gold tin (AuSn) can be found in the below chart.

This chart as well as more detail on gold tin (AuSn) applications are available in the paper titled, “Process and Reliability Advantages of AuSn Eutectic Die-Attach,” presented at IMAPS 2009.    

Ignoring the solder selection as part of your design process is risky business. 

As Terry Costlow, the IPC online editor of EMS Now noted in an article ‘Controlling the Explosion of Lead Free Solders’, the choice of the right solder alloy can affect the manufacturing process, the cost, and the field performance of the product.

Initially it was thought that the move to Pb free solders was just a matter of changing reflow profiles but major issues such as tin whiskers, brittle intermetallic layers and other concerns soon pushed solder selection into the forefront.

With over 200 published alloys and over 300 custom alloys shipped each year, we have seen the need for considering the solder design first.  Before you settle on a solder you have to consider:

·         Surface metallizations

·         Operational temperature of your product or device

·         Form of the solder you want to use (solder paste, solder preform, solder wire, etc.)

·         Temperature of subsequent soldering steps

·         Thermal coefficient of expansion

·         Tensile strength

And these are just a few of the considerations.  Let us help you make the right selection.  Contact us at: askus@indium.com.

Feel free to discuss solder selection with our industry professional, Dr. Lasky on November 11^th, IPC is having a materials conference: Engineering for Compliance in Irvine, CA.

A reader of this blog recently mentioned: "I am interested in what products could be sold by manufacturer's representatives."  That is a large question, considering the evolution that we have come to expect in the solar industry.  To answer that question involves first breaking up the industry into 2 separate sections, front and back end solar assembly.  Front end assembly involves the process of making the solar cell.  Back end involves connecting cells together and assembling them to create a useable device.

Both front and back end products are going to be geared to the customer's technology.  For instance, if I was purchasing materials for a large thin-film manufacturing company and someone boldly offered me glass filled high-temperature metallization paste, I would tell them to come back when they know what they are talking about.  (In reality, I'd be nice – even though it's an incredibly ignorant mistake.)  With that in mind, let's focus on what back end products a representative might be offering for crystalline and thin film solar customers – assuming that back end begins after metallization:

• Outsourced Solar Cells
• Tabbing Ribbon
• Bus Ribbon
• Tabbing Flux
• Solder Paste
• Preforms
• Solder Wire
• Tacky-type Fluxes
• Tabbing Equipment
• Rework Equipment
• Test Equipment/Services
• Packaging Materials
• Junction Boxes
• Laminate Materials
• Silicone/Sealing Materials
• Passive Components
• Ovens
• Frames
• Gloves / Lab Coats / Safety Equipment

I probably left out as many possible line items as I included, but I hope you get the idea.  Feel free to add the ones I forgot in the comment section below.

~Jim

Figure 1: 15% Voiding with air reflow

Figure 2: ~0% Voiding after vacuum reflow

Figure 3: Multiple voids

While at the Semicon West 2009 show in July, I had a chance to sit down with Herr Klaus Roemer of Pink GmbH. PINK is most famous in the die-attach and power module manufacturing world for their reflow ovens with vacuum, but are also known in the medical and aerospace industries for manufacturing extremely high precision, one-off, vacuum equipment for applications as diverse as particle-accelerators for ion bombardment, and large-volume chambers for helium leak-detection. I asked him some questions about Pink vacuum soldering technology.

Cheers! Andy

0402 or 0603 solder preforms deposited in paste for pin in paste assembly

Pin-in-paste is the technique of intrusive soldering through-hole components to a circuit board using reflow soldering.  Typically, solder paste can be printed and this will provide enough solder for complete barrel fill.  Occasionally, more solder is needed than can be printed, and solder preforms can be used.

Phil Zarrow and Jim Hall of ITM Consulting have a recorded discussion forum called "Board Talk" in which they discuss common board assembly issues and solutions.  One of the topics they have discussed is called, "Through Hole Reflow - Pin in Paste."  Here, they discuss the typical techniques used for soldering through-hole components to a circuit board.  These include printing solder paste around the through-hole in the board, inserting the through-hole connector, and reflowing the assembly in a convection oven. 

They mention that one way to apply more solder is to overprint the solder paste.  For many applications, this is an excellent technique.  The overprinted solder paste will wick into the barrel during the reflow stage.  This is a natural process because the over-printed area is typically a non-solderable solder mask surface outside the plated through-hole annular ring.  The solder de-wets from the solder mask and surface tension pulls it into the pool of solder, onto the annular ring, and down the plated barrel of the board.

Occasionally, overprinting solder paste still does not provide enough solder to fill the through-hole.  On these occasions, a good alternative is solder preforms.

There are a couple types of solder preforms to consider.  The first is a standard 0402 or 0603 size preform supplied in carrier tape.  These preforms are 100% metal compared with solder paste, which is only approximately 50% metal by volume.  To incorporate preforms, print solder past around the through-hole.  Place a preform just outside the annular ring, but touching the solder paste.  Just like overprinting, the solder preform supplies extra metal, but this time, the metal from the solder preform will wick down the through-hole barrel and provide much more solder than the overprint was able to.  The flux in the solder paste will be enough to remove oxides from the preform, so no additional flux is needed.

A second type of preform to consider for the most difficult-to-solder connectors are integrated preforms.  These preforms are custom-designed for each connector type and include an array of washers.  One washer will fit over every pin.  Flux is applied and the connector is inserted.  The assembly is reflowed in a convection oven, and more solder is available to fill the barrel than could be supplied using solder paste at all.  This is the most manual technique, however, may be the only option to achieve a complete barrel fill without re-designing the board.