My latest "buy" of Chinese BF981 Dual Gate Mosfets. - 20 percent
were defective parts. Discussion and photos of the testing follow:
Hamelectronic Magazine (dot com)
earlandrews.com -- they are mirror sites.

22 March 2014. New Article in Progress!
Below Pictured the ebay ad for 10 pcs for $14.15 US dollars. So I bought a lot of 3 of
these for a total of 30 pieces of the BF981. - Previously..I had bought 30 bf981s and
all 30 were defective. This time I am going with another seller to see how I fair.
So I paid $39.06 for 30 parts or about $1.35 each delivered. I sell these parts with my little on line sales service for $2.00 each (American Dollars).

Anyways.. I just tested the whole lot today March 22 2014. After testing I had 6 bad parts out of the 30 I had ordered or 20 percent defective parts.
Back in 1987 to 2004; I used to work in cataloguing and material management of Military parts and Mil Spec components. Mainly Microcircuits
(ICs) and Resistors. The Failure rate level of the Mil Spec Resistors was typically .001 pct failure rate level after a rigorous testing of 1,000 hours
of burn in. These parts by contrast had a 20 percent failure rate-- INFANT failure rate.

I don't think this is acceptable at all. Prior to 2014; I had purchased BF981s and I never tested them. I just always assumed that they would work..
that is until I received an email from a fellow in Nova Scotia who had some bad experiences with buying BF981s from Ebay.

HERE IS WHAT HE WROTE:   
 Earl,

I’ve just sent you $12.05 CAD for 5 transistors. Let me try them first.  If OK, I will order more.
Regards, MR. V
----------------------------------------------------------------------------------
Well..at first I thought he was overly cautious!
-------------------------------------------------------------------------------
Hi Earl,

I received your transistors today. I will be able to test them on Tuesday. I let you know.
Thank you for quick shipment.
MR> V.

then Mr. V wrote me again:

Hi Earl,
I’ve just sent you money for the second batch of transistors.
For testing FETs I made a small rig to measure static characteristics (Idss, Vgs cutoff, etc.) .
It’s an almost standard circuit: four smooth clips for connecting FET leads, two 9V batteries, two potentiometers to set voltage on gates, several
resistors to ground and reduce current on gates, alligator clips to connect mA-meter at the drain and V-meter at gates. The source is grounded.
An On-off switch. A LED to indicate ON  state. Switches can be added to switch polarity for a n or p type and a depletion or enhancement type.
MR. V.
-------------------------------------------------

Hi Earl,

This is MR. V from Bedford, Nova Scotia. Today I received my order. Thank you for prompt shipment.

All parts are good, except BF981 (5 pcs.).  I dealt with them on a piece of copper foil and tested them in my MOSFET tester.  Three transistors are
dead. Two are faulty: drain current does not change when gate 1 voltage changes.

Actually they are from a different batch compared to those you sent me before. Those (all working) were with marking printed on the silver face
and had a flat black back. These are all black and the back has a depression. I’ll send them back to you tomorrow so you can test them if you want.

Do you still have those silver-face BF981?
Regards, Mr. V

---------------------------------------------------------------------------------------------------------------------------------------------------------------------

THESE SILVER FACED BF 981s were from another batch that I had bought years ago. -- Mr. V was/is not being over-cautious in testing his
components. NOT AT ALL! -

At first I thought to myself..."this guy might be trying to rip me off!" -- I do have a gentlemans agreement on my web site that I will give you your
money back if the parts do not work!!! -- Maybe he will take the parts and just say they didn't work and get free dual gate mosfets.

SO..I STARTED DOING MY OWN TESTING AFTER MY SHIPMENTS TO MR. V -- and I'm not just "spot checking" the parts here and there... I was
going to do a 100 percent test of all items before shipping them out.. (if possible).  SOME PARTS are too complex to test..then I take my chances!

So..I bought a better tester and an IC tester as well and I have also started testing RF output transistors like the TO220 MRF476s, 2SC2270s and
others in my test jig with an HF RF low power driver transmitter.

TROUBLESOME TRANSISTORS FROM CHINA ARE: CB transmitter transistors (just look on youtube for the little movies of bad CB transistors!!)
Here is an article I wrote in 2013 about 40 RF transistors type 2SC2075 (C2075s) that were pure junk!!! I still have the bad transistors in a parts
bin. I didnt approach the company about them. I just swallowed the loss.
http://www.earlandrews.com/faketransistors.html .

Dual Gate Mosfets BF981s also seem to be TROUBLESOME !!!  --- The previous 30 BF981s I ordered from China were all BAD! 100 percent BAD!
You can read about this experience in an earlier article I wrote:  L
INK HERE: http://www.earlandrews.com/dgmosbad.html

----->> the 100 percent bad lot of 30 came from a company I actually like in China UT SOURCE. I havent stopped ordering from them either. I still
think they are pretty good BUT..there seems to be a problem with some of the parts they carry.

They were pretty good in dealing with me however. I sent them back the 25 of the 30 BF981s that I still had (the other 5 were with MR. V)
(MR. V sent them back to me eventually.. (I still have the 5 bad ones).  -- And UT SOURCE promised me to send my money back for the parts and
for the postage I incurred in mailing them back to them. --

SO....----------------->> I decided to try my luck with another company.. and I seen these
SILVER FACED BF981s - so I figured why not try them. This
company has a 30 or 60 day money back guarantee and so I felt I couldnt lose. Also..I would not give them a GOOD REVIEW until I had tested the parts.

NOW -- 22 MARCH 2014-- I am going to write the company tommorrow and tell them about this web page and the testing I have done. I will be
reporting the results here after Iam through.
I bought 3 lots of 10
Here are the 30 dg mosfets on the work table. I ground myself periodically to a
piece of test equipment nearby. I have found..through my own experience..
these BF981s are fairly rugged and there is no static electricity in my
basement shop. You can't blame these faults on static damage. The results of
my repetitive persistent testing cannot be attributed to something I am doing.
Above is the chart I made and always have in front of me when I test BF981s. Note the lower left
hand corner is another diagram of the layout of metal can ICs. -- I have tested 3N211s out of
China as well.
The good BF981s test as
per the screen below
This below is a bad BF981. This is common with bad ones. They test as a
resistor
Below: the actual resistance is (commonly) 29.2 Megohms or similar when bad
BF981s test as a resistance. What I do when I encounter these readings is tighten up
all the test lead connections and double check the layout and test a few more times
to be sure!
Below pictured the 6 bad dg mosfets. 6 out of 30 were defective. I have numbered
them in this case and will actually keep them stored with their numbers. I will store
them flat on a small piece of esd material -- QUESTION:
Does anyone have
sophisticated test equipment and/or wants to remove the die from the plastic to
examine what makes these items tick? -- or rather should I say... what makes these
items not tick?? - I am going to keep them in case someone can do some tests!
So..we have 6 defective dg mosfets BF981. Below are the numbered dg mosfets with their respective test screens.
Number one tests as a JFET. -- I double checked my connections and kept doing the
test and this is what resulted after repeat tests. - It is no surprise to me! - I have had
this screen with testing bf981s before. Not sure what is going on exactly BUT..it is
not testing as the majority of BF981s test (that is GOOD ONES!)
Bad BF981 number 2 tests with the resistance between the leads.
Nr. 3 tests as a capacitance between the leads.
Nr. 4 tests with this chinese lettering. NO SURPRISE. This is open
circuit or could be component not recognized or something like
that. Ive seen this one before (lots of times) when testing BF981s
Number 5 - once again the resistance measured between the two leads.
Finally..once again with nr. 6 - the jfet symbol. Not a surprise.
Above the yield of good ones - 24 good ones out of the shipment of 30 dual gate
mosfets that I purchased from China. -- HOW good are they? Well..thats a good
question. Sure they passed the test ..a basic test. Who knows if they used the correct
die or how the part was bonded. My wife used to work in the bonding room of a high
tech company. - Sometimes she would tell me of how they had problems bonding the
parts and sometimes there was contamination with the water -- ie think it was called DI
water.
The mil spec parts I used to work with (not directly but on paper and computer) had
high reliability ratings and they had to go "burn in testing" to MIL STD 883B. I think it
was 1,000 hours of burn in at high temperature and later they switched over to an
abreviated burn in of 160 hours (something like that) only at a higher temperature to
simulate 1,000 hours. These are ICs or Microcircuits. - REwork  of the die of Mil Spec
parts was not allowed. This according to my old boss at work.

In my opinion.. these parts are unacceptable. Most if not all of the BF981s in this test
should have been screened out at the testing stage. Not sure if they spot test or they
just let everything go as is or what.
Just to make sure of things..I went back and tested (again) some of my
old good dual gate mosfets and the good ones I screened out of this lot
of 30 and they measured as per above.

Ironically..this tester is from ebay/China. Im really pleased with the little
testers like the above one and some others I have purchased from ebay
and China. No complaints there. The testers are economical and they
work well.
SO I did get some of the money back on this lot of parts. Iam relatively happy. I now have 24 of the BF981s that work and test
good. So I will be selling them at $2 per part.

STAY TUNED TO MY WEB SITE. -- what I do..is I test my parts before I ship them out. --> SO ..if I uncover any more bad parts
through tests..I will write another article about it.

I know there are lots of posting about counterfeit parts on YOU TUBE and the web. One fellow in our radio club told me..I dont
care if they are counterfeit parts..just as long as they work!! -- Well..I am finding out..they are not only counterfeit but also they
are sometimes complete junk! Other times..they are hit and miss!

link
back to my home page www.earlandrews.com or www.hamelectronicsmagazine.com (these are mirror sites).
Dear earl1andrews,



Sorry,we sold a lot of it, no one say it's not good before yo u,what can we do for you?refund money? how much?thanks


All the best,
SamulWei
Dear smallpartsbigdifference,

20 percent of 30 BF981s are bad. I have documented the findings on my web page.. see the following page www dot earlandrews dot com/dgmosbadagn1 -
I am wondering what I should do next. I am not going to leave negative feedback..but I am going to have this article remain on my web site.

Earl (PS) I ordered 30 BF981s from another company(UT Source) and all of them were bad or defective. - I sell components from my web site. I test them now
to validate. see the web page and other related ones in my site. tnx earl

- earl1andrews
I wrote the company: smallpartsbigdifference -- and here is how that went....>>
Dear smallpartsbigdifference,

The refund amount of 20 percent of the original purchase would be OK. NOTE: Electronic components are complex devices and what often happens is people
will buy say 10 or 20 and put them in their parts bins and maybe use one or two here or there to fix something. I have been in Electronics since the year 1970.
Nowadays..we have more test instruments and with the internet..more people talk about problem parts. I have found BF981s coming out of China to be
problems. There is not adequet Quality Control on some of the parts being produced. Anyways.. something to consider. I am not against Chinese parts at all! -
I think that it is great what electronics are being produced from China. There just needs to be some adjustments made as to quality of the parts and quality
control. Thanks Earl Andrews

- earl1andrews
Dear earl1andrews,

Hello,we will do that tomorrow when back to office,thanks

All the best,
SamulWei