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Problems with TI DSP modules

Basaran

#17971

Problems with TI DSP modules | 22 October, 2001

Is there anybody in this forum who is using TI DSP 320C6203 modules for communication devices. I would like to know if anyone has problems with Solder bump- Ni pad interface delamination or problems with signal quality.?

Cemal Basaran

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#17974

Problems with TI DSP modules | 22 October, 2001

We on SMTnet have danced around this component package, but there is not a "background" of knowledge in the fine SMTnet Archives.

We in our company use this component package, but have not seen the problems you discuss. [We see other problems.]

This component package is a pain in a spot somewhat below the neck, because of the slug of metal used for a heat sink in the package. Issues are: * Process measurement needs to be measured on the solder balls [both at the inner row and the corner]. The difference in CTE of all the elements of this package can make it difficult to profile otherwise. * Process verfication with a standard xray machine is close to futile. Check the OnBoard Forum with Gil Zweig of Glennbrook Technologies.

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Cemal Basaran

#17979

Problems with TI DSP modules | 23 October, 2001

What is the reflow temperature you use to attach this package to your PCB.? I did extensive study on this package and compared it with other packages. I used our own Moire Interferometry, SEM, EDX studies. In my opinion the problem is TI does not manufacture it according to IPC-7530 spec. They reflow NiAu to eutectic PbSn at 225 with 5 sec hold. Spec temp and hold time are much higher. Intermetalic in this package is 2 micron versus 20 micron in a good package.

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#17982

Problems with TI DSP modules | 23 October, 2001

WOW!!! How do people get these coo toys?

Comments are: * IPC-7530 is not a specification. It is merely a guideline. [IPC-7530 �Guidelines for Temperature Profiling for Mass Soldering (Reflow and Wave)�] * What makes you say a 20-micron intermetallic is necessary in a good package? [er, words to that effect] We think a 2-micron intermetallic is fine. Help us understand this better, please. * Why isn�t a thinner intermetallic was better in the received component, since we�re just going to make it thicker as we reflow the board a couple of times?

Our profile for a TI TMS320C6XXXblablabla: * Preheat ramp: 2�C/sec to 140�C * Soak ramp: 0.2�C to 180�C * Time over liquidous: 90 sec * Peak: 215�C * Cool-down ramp: -3�C/sec

Let�s talk about your delamination at the nickel interface that you mention: * Is the delamination on the nickel of the interposer of the BGA or at your board? * What does the delaminated pad look like? * Is this delaminated surface solderable? * What�s your thinking on �black pad�?

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Cemal Basaran

#17986

Problems with TI DSP modules | 24 October, 2001

Dave; Thanks for responsding so fast. here are my answers.

1-WOW!!! How do people get these cool toys? I am with the University at Buffalo Electronic Packaging Lab. http://www.packaging.buffalo.edu We have pretty much everything that is sold on the market as well as Laser inspection technologies we develop in house. 2-* What makes you say a 20-micron intermetallic is necessary in a good package? Intermetallic is a metallic diffusion region. You need thermal energy to facilitate diffusion. When we compare good packages with bad packages we see that good packages (long fatigue life) have a thicker IMC region. We see a lot of packages from different manufacturers.

2-Why isn�t a thinner intermetallic was better in the received component, since we�re just going to make it thicker as we reflow the board a couple of times? No actually you don't reflow the previous IMC when you reflow the package on the board side. IMC from the previous preocess always and should have a higher melting point than the next reflow temp. If you did reflow the previous IMC you would not be able to control the positionig on the pad and you would have misregistered solder ball.

4- Is the delamination on the nickel of the interposer of the BGA or at your board? Delamination is between NiAu of the interposer of the BGA and Solder ball interface not at the board side. Essentially TI side since the module comes with solder bumps. 5- What does the delaminated pad look like? I can send you a SEM picture if you want. 6-Is this delaminated surface solderable? Never tried but oxidation and contamination would be a problem. 7-What�s your thinking on �black pad�? What do you mean by black pad. Different sectors in packaging industry use different terms for same things. I am sorry you have explain it a bit. Thanks very much

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#17990

Problems with TI DSP modules | 24 October, 2001

1- DF1: WOW!!! How do people get these cool toys? CB: I am with the University at Buffalo Electronic Packaging Lab. http://www.packaging.buffalo.edu We have pretty much everything that is sold on the market as well as Laser inspection technologies we develop in house. DF2: Nice picture. What do inspect with lasers? Is that part of that Moire Interferometry jazz?

2- DF1: What makes you say a 20-micron intermetallic is necessary in a good package? CB: Intermetallic is a metallic diffusion region. You need thermal energy to facilitate diffusion. When we compare good packages with bad packages we see that good packages (long fatigue life) have a thicker IMC region. We see a lot of packages from different manufacturers. DF2: Where has this been published? It is not conventional thinking. Conventionally, IMC are brittle and fatigue cracks appear along the lead interface to IMC interface when temperature cycles that are fast enough to bring enough shear stress in the intermetallics to break them. For instance, a CALCE study showed there is drop off in strength after the intermetallic thickness exceeds approximately 8-10 microns a standard Sn60 solder joint.

Taking a step backward, I�ve been generalizing about copper-tin IMC, which is wrong in this case. Hopefully there is no copper available to form an IMC on the top of the ball, where the nickel SB blocking all copper reactions. And there is no way a nickel-tin IMC could get anywhere near 2-micron thick, much less 20-micron. So, you must be talking a gold-tin IMC. * Gold-tin IMC can easily get to be 20-micron, but at that thickness it would be so brittle, it would fall from the board in a stiff breeze. * There�s no way that TI would intentionally give you enough gold to grow an IMC that thick.

So, I�m double confused!!! First point of confusion is this �thick IMC is better� thing. Second point of confusion is about the composition of the 20-micon IMC that you are seeing at the ball interposer interface.

3- DF1: Why isn�t a thinner intermetallic was better in the received component, since we�re just going to make it thicker as we reflow the board a couple of times? CB: No actually you don't reflow the previous IMC when you reflow the package on the board side. IMC from the previous process always and should have a higher melting point than the next reflow temp. If you did reflow the previous IMC you would not be able to control the positioning on the pad and you would have misregistered solder ball. DF2: Sorry, I didn't mean to suggest that IMC would melt at reflow temperatures. [I can still read my phase diagrams: Both Cu-Sn IMC melt above 415�C. Two of the three Au-Sn IMC melt above 309�C. The third Au-Sn IMC melts above 190�C, but it doesn't occur all that much.] The point had to do with both the exponential time dependence and Arrhenius temperature dependence of IMC growth, which at its nub says: the more you heat an IMC above absolute zero, the thicker it gets.

5- DF1: What does the delaminated pad look like? CB: I can send you a SEM picture if you want. DF2: I shudda known. I�ll take the SEM pix. What composition of materials do you get?

7- DF1: What�s your thinking on �black pad�? CB: What do you mean by black pad? Different sectors in packaging industry use different terms for same things. I am sorry you have to explain it a bit. DF2: Black pad just about counter-balances all the good things anyone can say about ENIG. The immersion gold works by corroding the nickel. If it is too aggressive, it takes away the nickel and leaves the phosphorous behind. This makes it look like the phosphorous level is too high [GT 9% w] in the nickel bath. Black pad can not be identified visually, you need to do surface analysis. What you will see is obvious dewetting. Since the nickel appears in varying shades of gray, it is commonly called "black pad".

Cogent black pad articles: Nick Biunno's article: http://www.nukcg.org/downloadfiles/Hadco%20on%20Immersion%20Gold%20failures.pdf George Milad's article: http://www.circuitree.com/ct/cda/articleinformation/features/bnp__features__item/0,2133,11666,00.html

However, let's not forget that dewetting can be caused by things other than those things traditionally associated with "black pad" (hyper corrosion of the nickel).

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Cemal Basaran

#17997

Problems with TI DSP modules | 25 October, 2001

We can inspect and measure strain field in anything larger than 320nm with Laser techniques we have. We can do this measurements during fatigue testing.

Of course thick intermetallic region as a solid region is a problem due to the fact that you have a brittle material right next to very soft solder bump. But I am talking about AuSn4 IMC. Gold intermetalics must be absorbed into bulk solder away from the interface that is what I mean by 20micron. I think in TI modules this AuSn4 is right at the interface 2 micron. because these modules are falling off the board when we try to cutt off a section from the board.

Yes there is little bit black pad in our EDX profiles.

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#17998

Problems with TI DSP modules | 25 October, 2001

You are correct.

So, the unit amount of gold [based on IG plating thickness, size of the pad, etc.] dissolves in the solder very quickly. When the solder is liquid for: * A long time, the gold disperses more. * A short time, the gold concentrates at the interface.

Yes. What you�re saying, about the gold being concentrated at the boundary and being more brittle, makes sense.

Why the gold is not dispersed GT 2um during the reflow heating cycle is the confusing part.

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