Jim Hisert’s Tech Support Blog
Recent Entries
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Package-on-Package Solder Paste for a High Yield Process
From a mechanical perspective, larger solder joints are generally preferred when assembling package-on-package (PoP) components. Just as a large set of gears can handle more power, fortified interconnects add a measure of reliability to BGAs and CSPs. That is why in many cases, paste is used instead of flux for package-on-package stacking - to increase solder joint volume. The added volume of solder helps keep the spheres in contact with interconnect pads throughout the reflow cycle, combating the effects of warpage. This will help you increase the final yield of your PoP assemblies.
Here are some links to learn more about the PoP paste process:
Control Your Materials, or They Will Control You (part 1)
Control Your Materials, or They Will Control You (part 2)
Package-on-Package Paste Leveling (1/5)
Package-on-Package Component Dipping (2/5)
Package-on-Package Transport (4/5)
Package-on-Package Reflow (5/5)
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Wafer Flux for a High Yield Process
Wafer fluxes seem pretty simple, just some liquid that helps form bumps on an electroplated wafer. The truth is that there are a lot of important quality measures that go on to ensure the highest quality flux possible. Low quality flux is like a fire cracker with a long fuse, just waiting to cause problems. Make sure you have wafer flux that is stable and predictable.
Wafer flux isn’t just a liquid flux to us. It is a semiconductor grade product that is treated as such throughout the raw material selection, design, manufacturing, and quality control steps. We know what is important to you, and the characteristics that need to be precisely controlled. Click on this link to get to a listing of wafer fluxes and other semiconductor grade fluxes.
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Ball Attach Flux for a High Yield Process
If you have been hoping that you current BGA process doesn’t fall victim to non-wets, it’s time to gain confidence. It sounds like you need a ball attach flux that is powerful. Those old solderability tests that define a flux’s wetting characteristics are done on clean copper. If you’re like the rest of the industry, I doubt you are using bare copper pads on your substrates. We know what works with different alloys on many various surfaces including Au/Sn, OSP, and Nickel (to name a few). Stop worrying about the flux you are using and give me a call @ (315) 853-4900 x7592.
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Solder Spheres for a High Yield Process
Surprises are rarely a good thing in production. High quality spheres minimize those ‘surprises’ when building BGAs and CSPs. ‘Zero defect spheres’ allow you to maintain a continuous build instead of stopping production for clogged sphere chambers, missing spheres, or non-wet failures.
Microsphere quality is especially important for bumping wafers. The dimensional tolerance of microspheres impacts the bump co-planarity across a wafer surface. In short, more precise spheres directly influence the quality of bumps on the die. This will of course increase your process yield since the spheres will all be closer to the pads they are being soldered to.
To learn more about precision solder spheres click here.
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Meet The Bloggers – An Interesting Mix
As mentioned last week, we are holding another Meet The Bloggers at SMTAI on Aug. 20th. If you are reading this and thinking “how does this relate to my semicon world?”, consider this: Even though SMTAI is an SMT focused event, these presenters are all top solder experts, and are going to be ready to talk about the things that have many parallels to our scaled-down world of silicon.
For instance, Amanda Hartnett specializes in interfacing and cooling flip-chips. Tim Jensen has extensive knowledge regarding the halogen-free craze that will be affecting which materials you use in the future. Dr. Ron Lasky keeps tabs on industry trends in technology. Anny Zhang knows first-hand the interaction of US and Asian manufacturing, while Rick Short is involved with shaping Indium Corporation’s presence in the Advanced Packaging market. We have a powerful team ready to hang out and chat with you, so I’d advise taking advantage of it if you’re in the area!
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Meet The Bloggers – Round 2
We had a pretty good turnout at Semicon West 2008 with our first “Meet the Bloggers” event, so we decided to try doing a similar thing for SMTAI Aug. 20th. The team has devised a list of starter topics including halogen-free, Ag concentration in alloys, and head-in-pillow defects.
Feel free to stop by the booth and discuss topics that are important to you!
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Filling in the Gaps
To see your process as a whole, you need to really understand your materials. I’ve known companies that teach us a thing or two about materials, but I’ve also worked with engineers who never test the materials they use outside of the normal process. It is obvious when issues arise, that engineers who do material classification ahead of time can react quickly to process changes. They know what they can rule out, how the process can change, and what to do to get a process back into control. Like a puzzle, the big picture is clear when you realize how all of your materials fit together.
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An Interview with Michael Qiu 采访邱学丞
Michael Qiu of Indium Corporation
邱学丞服务于铟泰中国华东区。采访他会是个从另一个角度去认识半导体行业的绝好机会。
Jim: How long have you been involved in the semiconductor industry in
吉姆：你在中国从事半导体行业多久了？
Michael: I have been in the semiconductor industry in
邱学丞：有三年多了。在这之前我花了四年时间在上海某大学学习IC设计、制造 (Fab)和封装。
Jim: What semiconductor materials are most popular for your customers?
吉姆：在你的客户中哪些半导体材料用的比较多？
Michael: For some semiconductor package customer, silver epoxy is very popular applied to do die attach. As for high power device, paste/SSDA is used popular for die attach. But for some advanced customers who do BGA, FC and WLCSP business, flux or fine power paste is required.
邱学丞：在一些封装厂里，银浆被大量地用来贴芯片于框架上。对那些做大功率器件的客户来说，锡膏或者焊线用来贴芯片比较普遍。而那些做BGA, FC和WLCSP的客户，他们需要的则是助焊剂或者精细颗粒锡膏。
Jim: What trends do you see in semiconductor package manufacturing in
吉姆：你觉得中国半导体封装的趋势如何？
Michael: For [cost sensitive] customers who do Diodes/Transistor package, the manufacture cost will be more and more important.
BGA/FC/CSP package share will increase soon in the near future and more factories will be able to do those packages.
More advanced package like SIP (system in a package) and MCM (multi-chip module) will [become] popular, but this may take several years.
邱学丞：对那些制造二极管或三极管的客户来说，成本对竞争力非常重要。他们对材料的成本以后会愈加敏感。在封装市场中，BGA/FC/CSP市场份额会有迅速的增长，而且会有更多的厂家能做这些封装。还有一些更高端的封装技术，比如SIP (system in a package) 和MCM (multi-chip module) 会开始流行，当然这得花个好几年时间。
Jim: What topics would our customers in
吉姆：中国的客户希望在半导体封装博克上看到什么样的话题？
Michael: Our customers always hope to get our professional technical support. They prefer the blog on a particular application or issue. For example, comparison between In and AuSn in LD die attach and use dilute hydrochloric acid to remove oxidation layer on In preforms.
邱学丞：我们的客户总是会希望能得到更好的专业支持。他们会比较喜欢主题明确，针某个具体应用或者问题的一些文章。比如：“LD芯片贴装应用中In和AuSn的对比”和“用弱盐酸去除铟焊片表面的氧化物”。
Jim: What is the most exciting thing about the semiconductor industry to you?
吉姆：半导体行业中什么东西最让你觉得激动？
Michael: A chip which is smaller than your nail has so many functions.
邱学丞：一个比你指甲还小的芯片能拥有如此多的功能，这太迷人了。
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Hardly Scrap – The Silicon Market
Are you giving away your broken and mis-registered wafers? …Probably not, if you realize the value of those thin silicon treasures. For those of us who like to work with unique wafers, finding a way to get our hands on different wafers can be a real challenge.
I’ve personally had around a 1:30 success rate in sourcing scrap wafers for non-customer related projects. Various issues make sourcing exotic wafers difficult. The #1 problem with contract bumping houses is that they are generally tied to contracts which require them to either return scrap or destroy it. This rule is intended to protect intellectual property.
The next hurdle is finding a potential supplier while they have the scrap on hand. If they tell you “I’ll let you know when we have some extras on hand”, I wouldn’t hold your breath.
Another roadblock is cost. Some scrap wafers and new wafers actually have similar price tags! Call me old fashion, but scrap wafers should be a low cost option for those of us who don’t need the integrated circuitry.
But if you’re still looking to sell scrap wafers, or if you can donate your wafers, I will take them off your hands and make sure they go to a good cause.
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Stock Up
I recently visited a customer to help optimize a flux-less indium soldering application. They admitted they needed flux but didn’t know 1) what to use, or 2) if there was a better way to fix the problem.
(Flashback 1 year…)
While having a technical discussion with a head engineer regarding future products, we agreed that it would be a good idea to have a water-soluble and a no-clean flux on hand for prototyping. He never mentioned that he was going to actually order the material, so I thought he would try it on an as-needed basis.
(Back to July 2008)
We were stuck in a situation where it would have been great to know the full issue ahead of time and send in the cavalry (ball attach fluxes), but we were a little blindsided since we actually were there for a different issue. I mentioned how it would have been great to carry in fluxes and they mentioned that they had a supply of Indium flux on hand! We were blessed with the luxury of having the best all-around ball attach fluxes right there for the indium thermal interface application.
These semiconductor grade tacky-type fluxes are worth every penny, they are like a Boy Scout’s Swiss Army knife. It worked for this customer, and having a small stock of multipurpose flux can work for you too.
Want to read more? Browse the archive of past entries.
