0
\$\begingroup\$

The part in question is a 2 x 2 mm LGA accelerometer.

1. First soldering scenario, 10% non working parts after the assembly:

  • no ESD protection gear
  • hot air gun smoothly brought near / away from above the part; low temperature & low air flow setting
  • care has been exercised in handling the parts

2. Second soldering scenario, 36% non working parts after the assembly:

  • wrist strap protection gear grounded to mains GND, nothing else
  • hot air gun not-so-smoothly brought near / away from below the part (from the other side of the PCB); high temperature & high air flow setting
  • care has not been exercised in handling the parts

I know ESD can damage such minute parts although I am not sure to what extent. 36% seems a bit high. Should I attribute this high rebuttal rate to the heating process ? Perhaps to something else ?

Responding to the comments

Care from the above paragraphs refers to directly touching the metal pins of the part or not. Probably not releveant ESD wise though. I should have been more clear on that, sorry.

As for the rest, I do not have a proper lab here, I am just hand assembling these PCBs at home. And the worst thing about this is that I do not have any temperature control. This is no bad soldering as re-soldering yields the same results. The rest of the circuit works OK once the faulty parts are removed. They have been kept in that special humidity absorbing bag they were shipped in.

\$\endgroup\$
  • 4
    \$\begingroup\$ I think 10% non working after assembly is high as well. Did you follow all precautions, recommendations, soldering profile as recommended in the datasheet? Did you investigate /prove that this component gets damaged? I mean, it could be a bad soldering connection, that would then exclude ESD. Regarding ESD: then something has to cause an ESD event, ESD does not happen "from nowhere". Also often ESD damage does not cause a component to fail immediately but only after some time, unless it is a very strong ESD pulse of course. \$\endgroup\$ – Bimpelrekkie Jan 19 '18 at 11:59
  • 1
    \$\begingroup\$ What kind of part is it? Some accelerometers using polymer micromachining might be sensitive to heat, though I am no authority on that. Have the parts been kept in a propper, dehumidified storage system, or been pre-heated to cook off any absorbed water before assembly? In addition, just strapping your wrist to ground isn't good enough, you need to have a high impedance (but not high enough to prevent dechargeing) to ground, otherwise any charge inside the PCB/chip will be able to transfer too rapidly to ground and cause damage. \$\endgroup\$ – Joren Vaes Jan 19 '18 at 12:02
  • \$\begingroup\$ Seriously!? You think 36% fallout is only "a bit" high? Even the 10% you mention first is well past unacceptable. \$\endgroup\$ – Olin Lathrop Jan 19 '18 at 12:10
  • \$\begingroup\$ This question is far too vague. "Care has (not) been exercised" could mean anything at all and conveys no information. More important: Are you sure that the part is damaged, or are you just getting bad solder joints? What kind of solder are you using and how are you applying it? Your description of the handling of the "hot air gun" suggests that you're not using proper rework technique. Is it even temperature controlled? \$\endgroup\$ – Dave Tweed Jan 19 '18 at 12:12
7
\$\begingroup\$

It makes no sense to ask us.

READ THE DATASHEET.

The datasheet will tell you the maximum temperature the part can withstand and for how long. For parts that are unusually sensitive to soldering, like some MEMS parts, there is also usually a recommended reflow temperature profile. Follow it or insist that your contract manufacturer follow it.

Some parts are difficult to solder by hand due to the solder temperature and time restrictions. You can do a few one-offs by hand and accept the failure rate. Someone really skilled with soldering that understands the issues can make a difference. But, for anything more than a few prototypes, you need to have these things soldered with temperature-controlled profiles.

Even your 10% failure rate is horrendous. There really is no excuse for that. From your description it's hard to say what exactly you are doing wrong, but the soldering temperature profile is my first suspicion.

\$\endgroup\$
3
\$\begingroup\$

As for the rest, I do not have a proper lab here, I am just hand assembling these PCBs at home. And the worst thing about this is that I do not have any temperature control.

Sounds like you have no proper equipment and required skills. 10% failure rate is a lot. In addition, depending on where you source components - they may be counterfeit or DOA.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.