Note 5. Purchased Intangible Assets and Goodwill

In 2012, in connection with our purchase of the serial flash memory product line assets from Atmel Corporation, we recorded $16.4 million of intangible assets.

In connection with the acquisition of S3 (Note 2), we recorded $15.3 million of intangible assets.

In connection with the acquisition of Echelon (Note 2), we recorded $17.7 million of intangible assets.

Intangible assets, net were as follows (in thousands):


			March 31, 2020
	Estimated Useful Life (in Years)	Gross Carrying Amount			Accumulated Amortization			Net Carrying Amount	Net Carrying Amount
Developed technology	4 - 10		$	16,032		$	7,734		$	8,298
Customer relationships	7 - 12			28,411			10,489			17,922
Customer backlog	1			2,779			2,779			—
Contract backlog	0.5			210			210			—
Non-compete agreement	2 - 5			662			635			27
Trademarks	8 - 12			1,290			217			1,073
Total intangible assets subject to amortization			$	49,384		$	22,064		$	27,320


		December 31, 2019
	Estimated Useful Life (in Years)	Gross Carrying Amount		Accumulated Amortization		Net Carrying Amount
Developed technology	4 - 10	$	16,032	$	6,905	$	9,127
Customer relationships	7 - 12		28,411		9,608		18,803
Customer backlog	1		2,779		2,779		—
Contract backlog	0.5		210		210		—
Non-compete agreement	2 - 5		662		588		74
Trademarks	8 - 12		1,290		186		1,104
Total intangible assets subject to amortization		$	49,384	$	20,276	$	29,108

We recorded amortization expense related to the acquisition-related intangible assets as follows (in thousands):


	Three Months Ended
	March 31,
	2020		2019
Operating expense category:
Research and development	$	828	$	828
Selling, general and administrative		960		960
Total	$	1,788	$	1,788

The estimated future amortization expense of acquisition-related intangible assets subject to amortization after September 30, 2019 is as follows (in thousands):


Year Ended December 31,
2020 (remaining 9 months)	$	5,249
2021		6,962
2022		6,070
2023		3,735
2024		3,463
Thereafter		1,841
Total	$	27,320