Indium Corporation Blogs

Following on from our discussions of last time...

As you will recall from the previous post on this topic, My friend and colleague Chris Nash and I were discussing some puzzling results for low dip height found during testing of package-on-package (PoP) materials. The findings will be of interest to everyone who uses a dipping process in both SMT and flip-chip assembly.

Post II:
For greater solder paste and flux dipping heights it appears as though a linear doctor blade (back and forth) used in a dipping process running at high speed will allow dip heights close to those expected from the theoretical engineered limit, for 50 microns and greater dip height. The high speed shear-thins the flux, which has the effect of both reducing the thickness of the boundary layer, and also has the benefit of reducing the extensional (tack) viscosity, so components can be more easily released from the dip tray.

What if you want to go to lower dip depths?

As we move into the area of copper pillar flip-chip dipping, and even (we hear) some Japanese customers doing package-on-package assembly, the dip height (dip depth) can go down to as low as 10-20microns, and this where we are hearing that rotary dip trays are coming into their own. The diagram below shows a simplified version of a flux and solder paste dipping tray.


Rotary dip trays seem to have the following advantages:

- Height Setting: The dip height/depth is set using two micrometers, so is infinitely adjustable to a precise setting, although the dip height does have to be measured.

- Low Cost: They also add zero capital cost for a new dip depth setting, compared to specially-engineered dipping trays, which can be upwards of $2,000 each.

- Accuracy and Precision of Depth: From a more pragmatic viewpoint, however, the real reason for rotary trays being used with ultra-low dip heights is that the flux depth is actually measured: there is no tacit assumption of a given dip depth being correct and constant, based on the engineering of the dipping tray. As we saw last time, an error of 20 microns is possible, and with a dip height of 50 microns or less, this is a huge problem if you are using a 50 micron dip tray and assuming that you are getting exactly that dip depth.

However, rotary dip trays also have their share of potential problems compared to linear dipping systems: 

 - Larger Surface Area: Flux and solder paste may dry out faster, and a water soluble material will be more vulnerable to the humidity content of the air. It is also more wasteful of flux, since a larger surface area of flux is exposed than will ever be used, although this may also be true of some of the linear tray designs.
 
- Circular Tray: Materials will experience a higher shear rate at the outer edge than in the middle. If spun too fast, dipping materials may accumulate at the edges, thrown outwards by centripetal force.

- Lower Shear Rate: For the same flux or solder paste dip depth, the velocity of the doctor blade will be much lower with a rotary than a linear system. However, as you can see from the illustration below, for a doctor blade moving at 1/4 the speed and 1/4 the dip height, the shear rate is the same.

As always, please contact me if you need to learn any more.

Cheers!  Andy

随着电子元器件组装微型化的趋势(miniaturization)，最近有越来越多的客户向我们咨询叠成封装的材料以及相关工艺(Package-on-Package；PoP)。

在向客户推荐PoP材料的时候，除非客户已经十分清楚自己要什么，我们一般会和他们详细介绍叠成封装焊锡膏PoP paste 和叠成封装助焊剂PoP flux具体是什么，分析各自的优缺点，然后让客户自己做决定。

Indium 公司的PoP paste (Indium9.88HF) 用的是5号金属粉，金属比重大概在80%-83%之间，根据是有铅还是无铅而定。 我们做过一系列的实验，和常规的SMT 3号粉和4号粉，各种金属比重的焊锡膏做比较，用5号粉在这个金属比重中做出来的PoP paste，各方面的性能最好。 Indium公司的PoP flux (Indium 89HF-LV) 也是根据各种实验结果都是最好的证实后， 才推出的。 通常检测PoP焊接材料， 可以做这三个实验： Transfer Test, Wetting Test, and Electrical Test. 具体的检测方法，Indium公司的Jim Hisert在他的论文中有详细描述。《Next Generation PoP Pastes for Electronics Assembly》

一般我个人比较喜欢推荐PoP paste，因为PoP paste能够提供extra solder。 PoP component本来就很薄，在焊接后回流的过程中十分容易“warpage 板翘”，那么component边缘部分就很有可能有一个上下之间很大的gap，导致根本无法形成良好的焊点。但是如果使用优良的PoP paste, paste中的extra solder metal 就能起到一个很好的“粘合剂”作用，即使有warage，也可以有一定的防御。 但是PoP flux在这方面就相对弱一点。

然而，PoP paste中的flux，因为要做很多功夫来清洗powder表面的氧化物，所以在回流过程中会有挺多的outgassing，这就很有可能导致空洞voiding 的产生。PoP flux相对而言，outgassing 就少很多，自然产生voiding的几率也小。

无论如何，优良的PoP paste and PoP flux，在防止wargage和voiding产生的defect方面，都是应该做得不错的。

Cheers!

Pic: Indium Corporation

Acknowledge to: Eric Bastow andJim Hisert with Indium Corporation  

A quick trip to discuss roadmapping with one of the world’s top processor manufacturers, and a visit to discuss Pb-free power die-attach materials, left me with a few hours to spare at LAX.

This time around I was trying to work out how much package-on-package (PoP) solder paste we would expect to see for a waferlevel CSP (WL-CSP) or a BGA dipped to half height. The need for some deep thought was driven by a customer who asked at what point a PoP dipping paste needs to go from a type 4 to type 5, 6, 7 and so on (however you define them), based on the PoP/CSP pitch or ball diameter. Good question.

To start with, in order to get consistent quantities of paste on each sphere, the PoP paste metal loading needs to be well below the point at which rheopectic behavior can expect to be seen (that is, much less than 50% by volume of solder powder metal). By doing this, you pretty much guarantee a “monolayer” of solder paste powder particles (radius r) coating the CSP or BGA sphere (radius R). Figure 1 shows the kind of result that is typical for a good paste: in this instance our halogen-free PoP paste Indium 9.88-HF.



Figure 1: 0.4mm pitch CSP with PoP paste

If the metal loading is too high, even at time zero, you will start seeing large variations in the amount of PoP solder paste adhering to the surface of each sphere (bump), even on adjacent spheres: the small amount of paste that is picked up during the dipping process adheres to the main solder sphere in uneven clumps. This is why standard type 4 printing solder pastes just don’t work in PoP applications: not only is the particle size too big – the rheology is all wrong.

If R>>r, then a reasonable first order approximation is that you can treat the sphere surface as planar and so model the number of solder particles based on a series of hexagonally close-packed particles (Figure 2 gives the definitions).
 

Figure 2: Definitions for the PoP paste dipping process

Using the same model of solder powder particle size as in the discussion on waferbumping paste, you can calculate a couple of potentially useful things:

i/ The maximum number of solder powder particles on each solder sphere (bump)

ii/ The mass of solder paste adhering to each soldersphere

The first (i/) is useful for establishing the inherent variability due to the finite size of the solder powder, and I’m going to suggest another Mackie rule of thumb of a minimum 150 solder powder particles per solder bump, based on the maximum allowed particle size (diameter). The table below gives  the result of this rather simplistic analysis:



Table: Effect of Package Bump Diameter on Solder Paste Type Needed

A 400micron bump should therefore be fine even with a type 3 dipping paste, whereas a 200micron bump will need a type 5 paste.

I look forward to someone proving this wrong. The second (ii/) is helpful, because we can easily use it to test the theoretical mass of PoP dipping paste against what we actually find. Note that this is just simple geometry: it doesn't tell us how much paste is really needed to resolve issues such as the 60 - 90micron bowing we are hearing about from our customers, even with the more rigid PoP packages currently available.

Cheers!  Andy

This week a customer in Asia asked why one of our new epoxy fluxes was not allowing the package-on-package (PoP) device to be picked up from the dipping tray. Obviously, the vacuum nozzle must have sufficient force to extract the PoP package from the PoP flux reservoir (yellow, below).



Those of you who know me also know that I am always trying to reduce things to numbers so, naturally I got thinking about how I would model this from a physical viewpoint and came up with the following:

If the downward force (weight of component plus tack force of epoxy flux) is greater than the upward force (air pressure on the bottom of the component), then the component could not be extracted from the epoxy flux. The figure shows the different variables. Expressing this mathematically, this comes out, in SI units, as:

Downward force = m.g + n.Ft.pi.(d/2)^2

where Ft is the tack force in units of mass per unit area, taken from the maximum tack force determined by the Solder Paste Tack Test from J-STD-005, ANSI/IPC TM 650:2.4.44

Upward force = 101000.A.pi.(D/2)^2

where A is the measure (fraction) of atmospheric pressure and denotes how good the vacuum is (zero vacuum is 0.0atm : hard vacuum is 1.0atm).

There are some uncertainties with this approach: How does the vacuum vary across the nozzle diameter? Does the 5mm diameter probe used in the IPC test equate to a complex CSP (chip-scale package) bottom surface, with many rounded solder bumps or solderspheres? And so on. But, at least the model puts us in the right ballpark. Just to give you a feel for how this works, the second figure shows some results. Note that scenario (iv) is the only one showing problems (negative force balance).

The data implies that you are only likely to see an issue with inability to pick up components from a dipping flux tray if either:

• Components: Heavy (thick / large)
• Vacuum Nozzle: Too small a diameter and/or the vacuum is weak/poor
• Flux: Very tacky (high tack force)

For many of the newer applications, component sphere/bump immersion to just deeper than the bump height (say 100-110%) is desirable. If the customer dips the whole bottom of the component into a standard (non-epoxy) flux, this potentially opens up a lot of issues including reliability (SIR; electrochemical migration); component displacement (skewing) during reflow; as well as difficulty in picking up the component from the tray. The solution to this series of issues, is to choose either a standard flux with a high pre-reflow SIR, such as our PoPflux 30B, or a low-volatile content epoxy flux.

I'll have more to say on epoxy fluxes in a couple of months, as we are currently nearing the end of extensive testing at several customers in Europe and Asia.

Folks,

My interest was piqued by a recent article from the pen of good friend, Ray Rasmussen. In this piece, Ray reviews a presentation by Phil Plonski of Prismark Partners on a tear down analysis of an Apple iPad. Ray comments on the profoundly dense interconnection, with package-on-package (PoP), flip-chip, etc. The result is a product with super-dense IC packing with a minimum of printed circuit boards (PCBs) needed. The micrograph, from Prismark, shows this impressive packaging design. 

Ray goes on to lament that these types of designs require fewer and fewer PCBs. He then states: “It won't be long before they learn how to build the iPad and iPhone without a PCB altogether.”

Whoa, slow down! Let’s think this statement through.

The PCB provides at least two fundamental functions:

1.      It provides mechanical support for the electronic components.

2.      It interconnects the components to each other and provides input/output connections so that the electronics can interact with the user.

(PCB experts will point out that there are many other functions such as heat transfer, electrical impedance matching, electromagnetic shielding, and a few other things the PCB provides in addition to those mentioned above. Many product designs require all of these functions of the PCB, however, even the most basic designs require 1 and 2.)

It is an imperative in any electrical design to minimize the number of components, PCBs, connectors, etc. in order to minimize cost and increase performance. However, the minimization of PCBs often results in those used becoming more complex and hence having more “value added.”

In looking at the micrograph cross section, one could strongly argue that the PCB has never been so important or so strongly a “partner” in the design. The multilevel, fine feature, high density interconnection provided by this PCB is truly a miracle of modern PCB manufacturing. Any other “PCB-less” design would require these functions and would essentially, by any other name, be a PCB. As an example, let’s say all of these functions were performed by the case of the electronic device. To manufacture this new PCB-less device, the processes that are used to make a PCB would be needed to form these functions in the product’s case.  In addition, solder paste printing, component placement and reflow soldering of the case would likely be a challenge!

So expect the PCB to be alive and well for some time to come…..and never more needed.

Cheers, 

Dr. Ron

最近小忙，少讀書了，也少和大家分享了；不過工作之餘，翻看了一下《A Seat at The Table》一書，覺得裏面有些道理也蠻有啓發的。比如説此書中一直圍繞這個主題來展開了論述“Today, the only thing your customer cares about is value.”

就這個觀點，再對照一下Indium公司的兩個主要系列產品：

²       電路板組裝焊接材料(Solder Materials):  這裡也要分產品而論。對於技術含量較高，工藝使用要求較多的焊錫膏(Solder Paste)材料，重視成品可靠性的客戶們會更多的關注產品帶來的“價值”。 如果只圖便宜的材料，但是用起來“錯漏百出”的，最後還是事倍功半：返工，復修，廢棄率高（特別是浪費貴的不能翻修的板子），產出率低，總體成本也自然高了。 對技術含量較低，工藝已經“模式化”的產品，像錫棒(Solder Bar)，錫綫(Solder Wire),  性价比會更關鍵……在目前日益高漲的金屬原材料市場中，Indium公司考慮到客戶們的成本壓力，也推出了性能可以和SAC305錫棒媲美的有成本優勢的Sn995錫棒。

²       半導體封裝材料(Semiconductor Materials):  整個半導體行業應該算是一個高成本，高投資，高回報（運營得好的話）的三高行業。半導體封裝材料也像是其中的經絡血脈吧，連接各個部分，讓整體最後順暢無阻的工作。半導體各個部分的材料都不便宜，設備更是不菲；對材料性能的表現要求和驗證都很嚴格，畢竟都投資那麽多，不能“功虧一簣”嘛。所以客戶們一般會十分重視產品的價值。 Indium 公司目前提供的半導體材料有：Wafer Flux, Wafer Paste, Micro Spheres, Flip-Chip Flux, Substrate Paste, Ball Attach Flux, Die-Attach Paste/Wire, PoP Fluxes, etc. 

Indium公司還為大家提供散熱界面材料(Thermal Interface Materials)，工程焊料(Engineering Solders)，薄膜光付太陽能板製造材料&太陽能板組裝焊接材料(PV Solar Materials)，和銦金屬及其化合物等。 這些材料使用在比較領先的應用中，新興行業，或是細分市場中，客戶們都十分重視產品和服務能給自己帶來的價值。

Cheers!  

Pic: Indium Corporation

PS: 前些日子看了中央4台的《第三屆漢語橋在華留學生漢語比賽》，感慨不已！除了感嘆這些留學生們對“那麽難”的漢語的精湛掌握，對中國文化和歷史的了解，甚至對中國的熱愛；更感慨的是，這些活動也説明了祖國的強大！現在越來越多的留學生們來中國學習，想進一步了解中國，和中國人民交流；中國話也在慢慢傳播到全世界！以前中國學子們苦讀英語，考TOFEL, 雅思，GRE什麽的；現在金髮碧眼的學生們也在場上比拼誰更了解我們的“四書五經”了，哈哈！

My friend and colleague, Eric Bastow, got back last month from an IPC standards meeting with some interesting news for those of us who supply and use solder paste. Here I’m talking about everything from standard SMT printing and Power Semiconductor die-attach solder paste (type 3 and 4) down to PoP and waferbumping solder pastes (type 5, 6, 7 etc). I had heard that there were some changes in the way the powder types are categorized and wanted to learn more. Here is what we discussed:

[Andy Mackie] What is the current status of solder powder “type” designations from the new IPC J-STD-006B (Oct 2009)?

[Eric Bastow] In the original J-STD-006B (Oct 2008) and its two amendments, a solder particle size distribution (PSD) table, Table 3-1, was included as part of the standard to define the different powder “types”: 3, 4, 5 and so on. However, this table has been removed from the version published exactly 1 year later (October 2009) and also, somewhat confusingly, called J-STD-006B. This latter standard refers the reader to the old J-STD-005 (Solder Paste) for powder type determination by PSD, tables 2A and 2B.

[Andy Mackie] So how are solder powder types currently (May 2010) defined by the IPC? 

[Eric Bastow] The responsibility for defining the powder size distribution for the respective types now goes by default to IPC Task Group 5-24b, which maintains the J-STD-005 and its amendments and associated documents. This standard and its amendment were created in the early 90’s, and then published in January 1995, when even type 4 paste was uncommon at best, so its relevance now in the second decade of the third millennium is rather questionable, particularly given the enormous changes in solder powder manufacturing methodology and analytical characterization that have occurred in that timeframe.

[Andy Mackie] I understand that there are even some concerns about the test methods used to define the PSD.

[Eric Bastow] Yes, very much so. It is interesting to note that the original J-STD-006B Table 3-1 recognized that “Types 5, 6 and 7 are shown as general industry accepted size ranges for development purposes. Current listed methods for measuring these particle sizes may not be accurate enough for exact size and range distribution”. That initial sentence is very revealing about the tentative nature of these “type” definitions. These same concerns were raised at the J-STD-005 meeting at APEX in April 2010, and I also raised issues about the relevance of the test methods (see below) that were in use.

Note that none of these addresses the possibility of pure solder powder being the sample.

[Andy Mackie] How did you and Indium Corporation drive the Solder Paste Task Group (5-24b) into the next phase?

[Eric Bastow] We realized that using 15year old test methods and standards for solder powder based exclusively on extraction from solder paste would raise serious concerns with our customers. As a start, Indium Corporation suggested round-robin testing amongst the various solder powder suppliers. The testing will involve the use of the in-house measurement techniques of those suppliers on representative powder samples from each of those suppliers, to see what sort of data scatter is observed. We helped the task group to recognize that defining the particle size distribution of the various types, especially the finer types, does not make much sense without first determining a reliable and repeatable method of measuring the particle size.

Once that is complete, we can begin to define what we mean by each powder type, and also if there is a need for such “hybrid” categorizations as type 4.5.

[Andy Mackie] Eric: thank you, and please keep up the good work.

===

The interesting thing is that it will not affect the way Indium Corporation supplies or manufactures solder powder and paste materials according to our customers’ needs: just how we define them.

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!

Click here for a description and video that shows a nozzle design from FINETECH  which clamps down onto PoP components during rework. 

“The PoP soldering head is an easy-to-use tool for reworking stacked devices as a whole in a single reflow process. It uses vacuum-actuated mechanical clamping tweezers which avoid separating the single layers of a PoP during component removal. The PoP soldering head can be easily adapted to different component thicknesses. Furthermore it is possible to adjust the width of the clamping tweezers prior to the process when the rework arm is swiveled down to avoid affecting other components on the PCB (e.g. accidental shifting of neighboring small passives).”

Sounds like this would be great for combating “PoP Quicksand”. That nasty problem that large components have when the vacuum provided by the nozzle isn’t strong enough to lift the package-on-package component back out of the PoP solder paste or dipping flux. Okay, I just made up that term – but it’s pretty descriptive, right?

Conceptually it seems to make a lot of sense, please comment if you have any experience with it!

7:40am

Just got in, fired up the laptop, and made some hot chocolate. This is the best time to get a jump on the day. I clear out my spam that rolled in overnight and prioritize the emails in my inbox. The first tasks that I cleared were:

-         Connected a new potential solar materials rep with the right people at Indium Corporation

-         Recommended the optimal reflow profile for Indium9.88HF PoP solder paste

-         Activated an online Vapor Deposition course

-         Helped specify tabbing ribbon and solder wire for a college student working on a lunar rover project

-         Planned underfill testing for today.

10:00am

After rounding up materials, components, and equipment, Brandon Judd and I assembled some BGAs on a customer's test board. Later today we’ll underfill, and rework some of the components to demonstrate the yield of a reworkable underfill. Each board had 18 components of 2 types. One of them is a very large, coarse pitch BGA. The other one (you guessed it) is exactly the opposite, a small, fine pitch BGA.

Noon

Took a drive and ate lunch.

1:00pm

When I returned to my desk, I noticed a few emails that needed attention. One was regarding the PoP solder paste reflow profile I mentioned earlier. It looks like that will work for the particular application. Another email regarded a barcode design that I am working on for a customer.

1:30pm

Took a call regarding solder sphere attachment. WS3622 was recommended to ease flux cleaning in place of an older tacky flux.

2:00pm

Answered an interesting call regarding thermal management for a cavity CPV assembly. The coolest part – he found my contact information on this blog.   

2:45pm

Worked on editing an interview for Global Solar Technology magazine. I had a chance to discuss many of our solar products in detail, while explaining the advantages of each.

3:00pm

The schedule for the day shifted, so we will reconvene the underfill testing early next week.  This gives me some time to begin the Interfacial Engineering course mentioned earlier. Looks pretty interesting so far.  Spent some time going through the course material and learning some new things.

4:30pm

Posted this blog entry. After looking at the things I’ve mentioned here, I noticed I could tweet all the little parts of my day. If you’re interested, check: http://twitter.com/SolderNinja

After just finishing her department’s monthly activity report, Patty took a break to stare out of her window, admiring the beauty of last night’s fresh snowfall. Her mind quickly went to the events of the past week. Rob had “popped the question” and Patty had quickly said yes. Her and Rob’s mothers were ecstatic. Both Patty and Rob liked and enjoyed each other’s parents. Patty recognized this as a blessed situation, but both mothers were now spending 10 hours each day planning the wedding. A result, Patty and Rob were both fielding 3 or 4 calls a day from each mom. Patty decided to go “with the flow” and count her blessings that both she and Rob had great parents.

She briefly looked down at the ring Rob had given her. It was a striking two carat emerald with 0.4 carat diamonds on either side. Rob was concerned that Patty might not like an emerald, but he explained that the price of diamonds is controlled and that “you could pave your driveway with diamonds for each equally good sapphire, ruby and especially emerald that exists in nature.” He went on to tell her that “all of the emerald mines of Colombia produce only one or two good 2 carat emeralds per year.”

Well one of them was right there on her finger. In addition to the uniqueness of emerald, the setting was in rhodium, the hardest and rarest of the precious metals. “Five hundred times more rare than gold,” Rob told her. She was especially impressed when she looked up rhodium on the internet and found this quote: “Rhodium has been used for honours, or to symbolize wealth, when more commonly used metals such as silver, gold, or platinum are deemed insufficient.” Gold and platinum insufficient!?

Rob was really secretive about how he found such an apparently rare ring. But it was consistent with his many other successes in life. She was thrilled to have him as a future hubby, even if she did beat him at golf. 

These happy and a little stressful thoughts were interrupted, by Pete coming to her door.

“Hey, kiddo, get packed, looks like will be going on another trip. Guadalajara, this time. Como es su espanol?” Pete said with gusto.

“Mi espanol es muy bueno. Why do you think we will go to Guadalajara?” Patty asked.

“Well, I just talked to Pedro and he said that they performed our productivity audit. Uptime is 29%, and all lines are time balanced to +/- 2%, about as best as could be hoped.”

Patty and her team developed a “Productivity Audit” from what they learned with The Professor in their recent adventures together.

“So then what is the problem?” Patty inquired.

Pete responded, “Jane, the finance exec we met on our trip to South Carolina, implemented a company-wide profitability software program. It was implemented and Guadalajara is 10% too low. No one can figure out why. I think we’ll want The Professor for this one.”

Patty called and was stunned that The Professor was again available. Apparently this was his off term teaching at Ivy University, as he teaches over the summer.  

When our trio arrived at ACME’s Guadalajara facility they all spoke in Spanish. Patty had taken Spanish starting in 4^th grade through high school, Spanish was one of the 7 or 8 languages The Professor spoke and Pete was second generation from Puerto Rico. They were surprised that the site GM, Harry Hopkins, asked them to speak in English.

“Give me a break, I grew up in Boston, I can barely speak English,” he joked in his heavy Boston accent. “We want you to help us find that lost 10%, we must be doing something wrong. Help us find it,” Harry implored. “One thing I can tell you is that I am really proud of my team, they are really working hard, you can tell by all of the product that is out there. It makes me proud just to walk out on the shop floor and see all of the product!”, he went on.

Patty was relieved that Harry was so supportive. Apparently Jane had sent the “good word” about how the trio had helped ACME’s South Carolina plant.

As the trio went on a tour, one thing immediately struck Patty, there was hardly room to walk around. There were partly assembled boards all over the place.

At the end of the tour Patty spoke up, “This facility is striking in how much partially completed product is on the shop floor.”

“And there-in lies the problem,”  responded The Professor.

How can profits be off when uptime and line balancing are so good? Could it be that Guadalajara uses poor performing solder paste, fluxes, or performs? Will our illustrious trio find the problem? Does Patty really like her emerald engagement ring? Stay tuned for the latest.

最近，公司在和一個原始設計商(ODM)公司談合作項目。

本來的初衷，是希望能給這傢ODM, 它的上游OEM（原始設備製造商）公司，下游EMS（製造加工廠），提供Indium公司性能穩定良好的SMT焊接材料(如錫膏solder paste，錫綫solder wires)等，並為他們提供及時的技術服務和一系列解決方案，協助他們做到最好。

但是在相互交流的過程中，我們了解到這傢公司還做IC設計，芯片曡層封裝等(Package on Package; PoP)。其實，在曡層封裝應用中，的Indium 公司也有的很成熟的半導體技術和材料。比如説for BGA/CSP的solder balls, dispensing paste/flux, transfer paste/flux, PoP paste/flux, etc. 

站在客戶端的角度，他們也應該希望有供應商能提供這一整套的解決方案，以對内外材料/技術的洞悉，幫助他們順利完成這個（些）大項目。

站在我們自己的角度，在協助客戶時，也最好有發現“交叉銷售Cross Selling”機會的眼睛， “发现销售不同产品或向不同部门（或客户）销售的机会，从而帮助客户，满足客户需求，达到销售目的。”

Cheers!

PS:  小帆這兩天在博客中寫到“操作系统的改进更新目前来讲都是小步前行。如若想像windows95/98那样革命性的变化，那就要看未来人机交互方式的变化。从某种意义上讲，硬件技术而不是软件技术将是未来变革到来的动力。比如，如果你能把电脑做成手表；如果你的输入设备能凭空展开或投射虚拟。。。”他的話語也讓我立刻想起現在電子行業的微型化(miniaturization)，芯片的曡層封裝，3D Dimension, etc. …..  科技以人爲本。很幸運，能生活在高科技的今天，享受各種高科技帶來的服務和便捷！

Source: Amkor



The new TVM™ PoP components have gotten a lot of press, and soon we should be able to get our hands on TMV PoP daisy chain parts for material testing.  I would love to evaluate next generation PoP solder pastes with these new components.  Lee Smith (Vice President of Business Development at Amkor) had this to say about obtaining parts for testing: 

LS: “We have significant direct and end customer demand for our TMV technology in next generation high density PoP applications.  Amkor has qualified the technology for high volume production and we are now completing customer ramp readiness and SMT validations.

In addition to our customer specific work, we have presented 3 TMV joint project studies on SMT stacking and board level reliability at industry conferences over the past 2 years.  We have demonstrated robust SMT stacking with standard dipping flux, paste and BGA underfill materials.  We plan on offering a 14x14mm daisy chain TMV PoP test vehicle through Practical Components sometime in Q2 2010.  Prior to that we will entertain joint projects with this test vehicle under non-disclosure agreements to validate compatibility with new SMT materials.”

Click here to learn more about the Amkor’s TMV and PoP package family.

For more information, Lee can be contacted at Lee.Smith@amkor.com

TMV is a trade mark of Amkor Technology, Inc.

Dr. Andy Mackie recently put together a model to determine the probability that a component can be successfully dipped in solder paste or flux.  Here is a little more from him on this subject:

"A customer in Asia was asking why one of our no-clean package-on-package fluxes, the ultralow residue NC510, was not allowing the PoP device to be picked up from the dipping tray. It turned out that the customer was allowing the flux to coat the whole of the bottom of the component, not just the solder bumps, so the vacuum nozzle had insufficient force to extract the PoP package from the flux . I got thinking about how I would model this from a physical viewpoint.

If the downward force (weight of component plus tack of flux) is greater than the upward force (air pressure on the bottom of the component), then the component could not be extracted from the flux. The figure shows the different variables. Expressing this mathematically, this comes out, in SI units, as:

Downward force = m.g + n.Ft.pi.(d/2)^2

where Ft is the tack force in units of mass per unit area, taken from the maximum tack force determined by the Tack Test Method from J-STD-005, ANSI/IPC TM 650:2.4.44

Upward force = 101000.A.pi.(D/2)^2

where A is the measure (fraction) of atmospheric pressure and denotes how good the vacuum is (zero vacuum is 0.0 : hard vacuum is 1.0).

There are some uncertainties with this approach: How does the vacuum vary across the nozzle diameter? Does the 5mm diameter flat IPC probe equate to a much smaller sphere? and so on, but it at least puts us in the right ballpark.
Just to give you a feel for how this works, the second figure shows some data. Note that scenario iv is the only one showing problems (negative force balance).  The data implies that you are only likely to see an issue with inability to pick up PoP components from a dipping PoP flux tray if either:

- Components: Heavy and have many large PoP solder bumps
- Vacuum Nozzle: Too small and the vacuum is weak/poor
- Flux: Very tacky (high tack force)

and certainly, if the customer dips the whole bottom of the component into the flux, this opens up a lot of issues, including reliability (SIR); component displacement during reflow; as well as inability to pick up the component from the tray. This is why we always recommend a flux dipping height of 40-50% of the PoP bump height, to eliminate these issues."

I have found this model not only interesting, but useful for technicians to use when asked why components are 'only dipped 50%'.  As a technician, it is good to have a scientific reason to refer to - even though experience may have already proven the theory to us personally. 

Brandon Judd and I have been working on a paper for this year’s SMTAI event, and I thought I would share a snip from it.  Although people generally share the beginning of a paper, I’d like to share the conclusion, in Brandon’s words:

“With the miniaturization of today’s electronic devices and the increasing complexity of their features, the need for PoP components is significantly increasing.  Although it may seem like a simple solution to just use the standard SMT paste that you have in-house for your upcoming PoP applications, these products will not be optimal for this type of process.  As our testing has shown, modern PoP solder paste materials are much better suited to the dipping process used for PoP components.  Formulation, particle size, and metal loading are all key factors in the design of a PoP specific paste.  The time spent evaluating these new products is well worth saving yourself the headaches of getting electrical opens on your boards from using standard SMT materials or even outdated dipping pastes, causing costly and time consuming rework down the road.  With the proper material and process, insufficient solder transfer and head-in-pillow defects should be a thing of the past.  “   

This is something you may have run into if you’ve ever manually dipped and placed PoP components.  Yesterday while trying to hold a conversation about the package-on-package process, I lost track of the very same process I was discussing.  I neglected to dip one of the components into solder paste before placing it on the board.  This is a picture of what happens.  The stack itself soldered well, as would be expected, but fell off when the board was lifted from the conveyor at the end of the line. 

If you’re wondering what a small error like this costs:

1 hour lost time + price of the board and components.

Luckily the other 14 PoP stacks can still be used for cross-sectioning and learning more about the PoP paste that was being evaluated.  If this was a production board I would be able to simply dip the stack and re-place it on the pads, send it through a second reflow, and test the final assembly for functionality – but you just can’t get away with that during evaluation.