SO642 Equivalent & Substitute Parts

Part Overview

The STMicroelectronics SO642 is an NPN bipolar junction transistor (BJT) rated for 300 V collector-emitter breakdown voltage and 100 mA maximum collector current in a surface mount SOT-23-3 package. This device is classified as obsolete, indicating it is no longer in active production. Finding equivalent and substitute parts is necessary to support ongoing maintenance, repair, and redesign activities for applications currently utilizing this component.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	300	V
Current - Collector (Ic) (Max)	100	mA
Vce Saturation (Max) @ Ib, Ic	500mV @ 2mA, 20mA	—
DC Current Gain (hFE) (Min) @ Ic, Vce	40 @ 30mA, 10V	—
Power - Max	310	mW
Frequency - Transition	50	MHz
Operating Temperature (TJ)	150	°C
Package / Case	SOT-23-3	—
Mounting Type	Surface Mount	—
RoHS Status	ROHS3 Compliant	—
Moisture Sensitivity Level (MSL)	1 (Unlimited)	—

Substitute Part Grouping Explanation

Substitute parts for the SO642 are classified into two categories based on electrical parameter alignment:

Direct Substitutes maintain all critical electrical parameters within the same operating envelope:

Voltage - Collector Emitter Breakdown: 300 V
Current - Collector (Ic) (Max): 100 mA
Vce Saturation (Max) @ Ib, Ic: 500mV @ 2mA, 20mA
DC Current Gain (hFE) (Min) @ Ic, Vce: 40 @ 30mA, 10V
Frequency - Transition: 50 MHz
Package / Case: SOT-23-3 compatible

Similar Substitutes share the same voltage and package specifications but differ in one or more of the following parameters: maximum collector current, power dissipation, transition frequency, or saturation voltage characteristics. These parts are suitable for applications where the specific parameter deviation does not impact circuit performance.

Parameter Comparison

Part Number	Manufacturer	Ic (Max) mA	Vce(br) V	Vce Sat @ Ib, Ic	hFE (Min) @ Ic, Vce	Power (Max) mW	Freq (MHz)	Package	Status
SO642	STMicroelectronics	100	300	500mV @ 2mA, 20mA	40 @ 30mA, 10V	310	50	SOT-23-3	Obsolete
MMBTA42,215	Nexperia USA Inc.	100	300	500mV @ 2mA, 20mA	40 @ 30mA, 10V	250	50	SOT-23-3	Active
PMBTA42,215	Nexperia USA Inc.	100	300	500mV @ 2mA, 20mA	40 @ 30mA, 10V	250	50	SOT-23-3	Active
2SC4061KT146N	Rohm Semiconductor	100	300	2V @ 5mA, 50mA	56 @ 10mA, 10V	200	100	SOT-23-3	Active
BF820,215	Nexperia USA Inc.	50	300	600mV @ 5mA, 30mA	50 @ 25mA, 20V	250	60	SOT-23-3	Active
BF820,235	Nexperia USA Inc.	50	300	600mV @ 5mA, 30mA	50 @ 25mA, 20V	250	60	SOT-23-3	Active
BF822,215	Nexperia USA Inc.	50	250	600mV @ 5mA, 30mA	50 @ 25mA, 20V	250	60	SOT-23-3	Active
BSS64,215	Nexperia USA Inc.	100	80	200mV @ 15mA, 50mA	20 @ 10mA, 1V	250	100	SOT-23-3	Not For New Designs
FMMT497TA	Diodes Incorporated	500	300	300mV @ 25mA, 250mA	80 @ 100mA, 10V	500	75	SOT-23-3	Active
FMMT6517TA	Diodes Incorporated	500	350	1V @ 5mA, 50mA	20 @ 50mA, 10V	330	50	SOT-23-3	Active
FMMTA42TA	Diodes Incorporated	200	300	500mV @ 2mA, 20mA	40 @ 30mA, 10V	330	50	SOT-23-3	Active

Engineering Selection Recommendations

Direct Substitutes (Recommended for Pin-Compatible Replacement)

The MMBTA42,215 and PMBTA42,215 from Nexperia USA Inc. are direct electrical equivalents to the SO642. Both parts maintain identical voltage, current, saturation voltage, and gain specifications. The PMBTA42,215 carries AEC-Q101 automotive qualification, making it suitable for applications requiring automotive-grade components. Both parts are in active production status, ensuring long-term availability. The MMBTA42,215 is available in higher inventory quantities (9885 Pcs) compared to PMBTA42,215 (3718 Pcs).

Similar Substitutes (Application-Dependent Selection)

The FMMTA42TA from Diodes Incorporated provides electrical compatibility with the SO642 across all critical parameters (300 V, 100 mA maximum at saturation point, 50 MHz transition frequency, identical gain specification). This part offers higher maximum collector current capability (200 mA) and increased power dissipation (330 mW), making it suitable for applications requiring additional current headroom. The part is in active production with substantial inventory (18404 Pcs).

The 2SC4061KT146N from Rohm Semiconductor maintains the 300 V voltage and 100 mA current ratings but exhibits higher transition frequency (100 MHz) and different saturation characteristics. This part is suitable for applications where improved high-frequency performance is beneficial.

The BF820,215 and BF820,235 from Nexperia USA Inc. are suitable for applications where collector current requirements do not exceed 50 mA. Both parts maintain 300 V voltage rating and 50 MHz transition frequency. The BF820,235 has significantly higher inventory availability (30577 Pcs).

Parts Not Recommended for New Designs

The BSS64,215 is classified as "Not For New Designs" and should not be selected for new applications despite its active inventory status. The BF822,215 has a reduced voltage rating (250 V) compared to the SO642 (300 V) and is suitable only for applications with lower voltage requirements.

Compliance and Regulatory Status

All recommended substitute parts are ROHS3 compliant and REACH unaffected, matching the regulatory status of the SO642. All parts maintain MSL Level 1 (Unlimited) moisture sensitivity classification.

Frequently Asked Questions (FAQ)

Q: Can MMBTA42,215 be used as a direct replacement for SO642 in existing designs?

A: Yes. The MMBTA42,215 maintains identical electrical specifications for voltage (300 V), collector current (100 mA), saturation voltage (500mV @ 2mA, 20mA), DC current gain (40 @ 30mA, 10V), and transition frequency (50 MHz). The package is SOT-23-3 compatible. The only difference is reduced maximum power dissipation (250 mW vs. 310 mW), which is not a limiting factor in most applications.

Q: What is the difference between MMBTA42,215 and PMBTA42,215?

A: Both parts are electrically identical. The PMBTA42,215 carries AEC-Q101 automotive qualification, making it suitable for automotive applications. The MMBTA42,215 is the standard industrial-grade equivalent. Selection depends on application requirements for automotive qualification.

Q: Why is FMMTA42TA listed as a similar substitute rather than a direct substitute?

A: The FMMTA42TA has a maximum collector current rating of 200 mA, which exceeds the SO642 specification of 100 mA. While this provides additional current capability, it represents a parameter deviation from the original specification. Applications designed for 100 mA operation can use this part without issue, but it is not a pin-for-pin electrical equivalent.

Q: Can BF820,215 be used in applications requiring 100 mA collector current?

A: No. The BF820,215 has a maximum collector current rating of 50 mA, which is insufficient for applications designed for the SO642's 100 mA capability. This part is suitable only for applications with collector current requirements not exceeding 50 mA.

Q: Are all substitute parts available in the same packaging as SO642?

A: Yes. All listed substitute parts use the SOT-23-3 package (also designated TO-236-3 or SC-59), which is physically and electrically compatible with the SO642 package.

Q: What is the inventory status for each substitute part?

A: MMBTA42,215 has 9885 Pcs in stock. PMBTA42,215 has 3718 Pcs. FMMTA42TA has 18404 Pcs. BF820,235 has 30577 Pcs. All recommended parts are in active production with adequate inventory for procurement.

Q: Does the reduced power dissipation of MMBTA42,215 (250 mW vs. 310 mW) affect circuit performance?

A: The reduced power rating indicates lower thermal dissipation capability. In applications where the SO642 operates near its 310 mW maximum, thermal analysis is required to confirm the MMBTA42,215 remains within safe operating limits. For most standard applications operating well below maximum power ratings, this difference is not limiting.

Q: Can 2SC4061KT146N be used as a substitute despite different saturation voltage specifications?

A: The 2SC4061KT146N has significantly different saturation voltage characteristics (2V @ 5mA, 50mA vs. 500mV @ 2mA, 20mA). This part is suitable only for applications where saturation voltage is not a critical design parameter. Applications requiring low saturation voltage for switching or amplification should use MMBTA42,215 or PMBTA42,215 instead.

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