LMZ10501 reliability

Hi Daniel,

As promised, here are the answers to your list of questions.

1) What happens to the exposed die after a long time in a humid environment?

The LMZ10500/01 nano module has passed the Temperature Humidity Bias Test (THBT) to 1000 hrs @ 85°C/ 85%RH, the Highly Accelerated Stress Test (HAST) to 96hrs @ 130°C/85%RH/33.3psia, and the Auto Clave (ACLV) Test to 96 hrs @ 121°C/100%RH/2atm.  

 2) Can dust particles or other contaminants that accumulate on the die over time cause any damage?

While “other contaminants” is a very broad term, this package has passed moisture related corrosion resistance tests including ACLV, HAST, and THBT per commercial grade qualification.

3) Are there any concerns when placing the device on a PCB? Are the standard SMT placing tools & methods suitable for the nano-module?

The LMZ10500/1 nano module can be manufactured with standard pick and place machinery used for microSMD or wafer chip scale packaging with some considerations:

• Use a small nozzle with 0.65mm diameter or smaller
• Use a soft tip pick and place head
• Slow the pick arm when picking or placing
• Add 0.05mm to the component height
• Placement force should be as small as possible, prefer less than 3 Newton

 Here is an applications note on handling exposed die packages:

http://www.ti.com/lit/an/snva009ab/snva009ab.pdf

 Also, we have created a video about “How to Solder Rework Nano Module Packages”:

http://www.ti.com/ww/en/simple_switcher_dc_dc_converters/power_module_videos.html

4) There seems to be some kind of a protective layer on top of the die. What is this layer? Was its long-time reliability tested?

There is no protective layer on the die, it is bare silicon. The entire unit (silicon and inductor) passed Operating Life Test (OPL) 150°C to over 950 hrs.  

5) After assembling PCBs, the boards are usually washed. Were the effects of PCB cleaning chemicals on the exposed die tested?

In building up several thousand evaluation boards for promotion and customer sample, we used a PCB washing process and did not experience any issues related to washing the boards.

6) The nano-module is soldered to the PCB by a reflow process. That means that the die on top of the module is "double-reflowed". Can't this second reflow weaken the connection of the die to the inductor? Are there any special reflow procedures for the module?

The nano module can withstand 3 reflows at 250 deg C for 10 seconds, peaking at 260 deg C.

7) What is the composition of the solder bumps on the die? If they are lead-free, is there a tin-whisker problem?

Here is a link to the chemical composition of the LMZ10500/1: http://www.national.com/green/pdf/LMZ10501SENOPB.pdf

They are lead-free per ROHS compliance; we have not had any tin whiskering problems.

8) Is it recommended to protect the die by applying some kind of an encapsulation on it? Were there any tests done to understand the effect of an encapsulation on the device? If so what is the recommended protection for the device?

Some customers use conformal coating in their applications and we have evaluated conformal coating over this package. The coating that we have used is from Dow Corning P/N 1-2577. We have ran TMCL and humidity and they all passed.

9) Was the module tested for mechanical shocks before and after soldering to a PCB?

It was subject to Board Level Reliability (BLR) drop test at 1500g, 1.0 ms and passed up to 100 drops.

If there are any reliability test data available that can be shared, I'd appreciate it.

Our reliability team is working on publishing an external report, we will post it on the Files tab of this SIMPLE SWITCHER® Forum.

Best Regards,

Denislav

Hello Kevin, 

I got a reply from our packaging folks. See below in blue.

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We don’t have any specific recommendation on underfill. Concern about underfill is CTE mismatch that may end up lifting/stressing the die in heated environment. CTE is a critical consideration when choosing underfill.

“Glop top” is fine, but process must be well controlled to avoid excessive amount being applied. We use the same back coating material for glop top. That is Hysol 1062. It is an epoxy based material. 

Encapsulation without underfilling the micro SMD is fine too.

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Regards, 

Denislav