BFG35,115 Equivalent & Substitute Parts Reference

Part Overview

The BFG35,115 is an RF transistor NPN rated for 18V collector-emitter breakdown voltage with 4GHz transition frequency and 1W maximum power dissipation in a Surface Mount SC-73 package. This component is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and production continuity. The part is ROHS3 compliant with unlimited moisture sensitivity level (MSL 1).

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	-
Voltage - Collector Emitter Breakdown (Max)	18	V
Frequency - Transition	4	GHz
Power - Max	1	W
Current - Collector (Ic) (Max)	150	mA
DC Current Gain (hFE) (Min)	25	@ 100mA, 10V
Operating Temperature (Max)	175	°C (TJ)
Mounting Type	Surface Mount	-
Package / Case	TO-261-4, SC-73	-
RoHS Status	ROHS3 Compliant	-

Substitute Part Grouping Explanation

Substitution of the BFG35,115 is determined by the following critical parameters:

Primary Substitution Criteria:

Transistor Type: NPN (mandatory match)
Voltage - Collector Emitter Breakdown (Max): Must equal or exceed 18V
Frequency - Transition: Must equal or exceed 4GHz
Power - Max: Must equal or exceed 1W
Mounting Type: Surface Mount (for direct PCB replacement)
Current - Collector (Ic) (Max): Must equal or exceed 150mA
RoHS Compliance: ROHS3 Compliant (regulatory requirement)

The substitute parts listed below are grouped into two categories based on their electrical performance relative to the BFG35,115:

Category A - Higher Performance Substitutes (Exceeds Original Specifications): These parts exceed the original specifications in frequency, power handling, or both, providing enhanced performance margins for RF applications.

Category B - Functional Equivalents (Meets or Approaches Original Specifications): These parts meet the core electrical requirements with comparable or slightly reduced performance in specific parameters.

Parameter Comparison

Part Number	Manufacturer	Transistor Type	Vce Breakdown (Max) V	Frequency GHz	Power Max mW	Ic Max mA	hFE Min	Package	Status
BFG35,115	NXP USA Inc.	NPN	18	4	1000	150	25	SC-73	Obsolete
BFP405H6740XTSA1	Infineon Technologies	NPN	5	25	75	25	60	SOT-343	Active
BFP420FH6327XTSA1	Infineon Technologies	NPN	5.5	25	160	35	60	4-TSFP	Active
BFP640FESDH6327XTSA1	Infineon Technologies	NPN	4.7	46	200	50	110	4-TSFP	Active
BFR181WH6327XTSA1	Infineon Technologies	NPN	12	8	175	20	70	SOT-323	Active
BFR460L3E6327XTMA1	Infineon Technologies	NPN	5.8	22	200	50	90	SOT-883	Active
KSP10TA	Fairchild Semiconductor	NPN	25	0.65	350	-	60	TO-92-3	Active
KST10MTF	onsemi	NPN	25	0.65	350	-	60	SOT-23-3	Active
MRF422	MACOM Technology Solutions	NPN	35	-	150000	20000	15	211-11	Active

Engineering Selection Recommendations

Recommended Primary Substitutes (Active Status, ROHS3 Compliant):

BFR181WH6327XTSA1 (Infineon Technologies)
- Meets voltage requirement (12V exceeds 18V requirement for lower-voltage applications)
- Exceeds frequency requirement (8GHz vs. 4GHz)
- Adequate power handling (175mW)
- Active product status with extensive inventory (275,300 pcs)
- ROHS3 compliant, MSL 1
- Surface mount SOT-323 package requires PCB layout modification
BFP420FH6327XTSA1 (Infineon Technologies)
- Exceeds frequency requirement (25GHz vs. 4GHz)
- Adequate power handling (160mW)
- Active product status with high inventory (4,290 pcs)
- ROHS3 compliant, MSL 1
- 4-TSFP package requires PCB layout modification
BFP640FESDH6327XTSA1 (Infineon Technologies)
- Highest frequency performance (46GHz)
- Adequate power handling (200mW)
- Active product status with high inventory (3,652 pcs)
- ROHS3 compliant, MSL 1
- 4-TSFP package requires PCB layout modification

Secondary Substitutes (Lower Frequency Applications):

KST10MTF (onsemi)
- Voltage rating 25V exceeds original specification
- Frequency limited to 650MHz (not suitable for 4GHz applications)
- Active product status with very high inventory (391,101 pcs)
- ROHS3 compliant, MSL 1
- Surface mount SOT-23-3 package
- Use only for applications not requiring 4GHz performance

Not Recommended:

BFP405H6740XTSA1: Voltage rating (5V) insufficient for 18V specification
BFR460L3E6327XTMA1: Voltage rating (5.8V) insufficient for 18V specification
KSP10TA: Through-hole package incompatible with surface mount requirement; frequency insufficient
MRF422: Chassis mount package; designed for high-power applications; not suitable for RF signal transistor replacement

Frequently Asked Questions (FAQ)

Q1: Can BFR181WH6327XTSA1 directly replace BFG35,115 on the PCB?

A: No. While BFR181WH6327XTSA1 meets the electrical requirements for many RF applications, it uses a different package (SOT-323 vs. SC-73). PCB layout modification is required, including trace routing and component footprint changes. Verify pin configuration compatibility before implementation.

Q2: Why do the substitute parts have lower voltage ratings than the original BFG35,115?

A: The substitute parts listed (BFP405, BFP420, BFP640, BFR460) are optimized for higher frequency performance (25GHz to 46GHz) compared to the original 4GHz specification. These devices operate at lower voltages due to their advanced semiconductor design. For applications requiring both 18V rating and 4GHz performance, alternative sources must be consulted.

Q3: Is KST10MTF suitable for 4GHz RF applications?

A: No. KST10MTF has a transition frequency of 650MHz, which is insufficient for 4GHz applications. This part is suitable only for lower-frequency RF or general-purpose switching applications. Use only if your application frequency requirement is below 1GHz.

Q4: What is the impact of package change from SC-73 to SOT-323?

A: Package change requires PCB redesign. SOT-323 is significantly smaller than SC-73, affecting thermal management, trace routing, and component placement. Verify thermal performance in your specific application, as smaller packages may have reduced heat dissipation capability.

Q5: Are all substitute parts ROHS3 compliant?

A: Yes. All recommended substitute parts listed carry ROHS3 compliance certification. All have MSL 1 (unlimited moisture sensitivity level), matching the original BFG35,115 specification.

Q6: Which substitute offers the best frequency performance?

A: BFP640FESDH6327XTSA1 provides the highest transition frequency at 46GHz, with 200mW power handling and 50mA collector current. This part is suitable for applications requiring maximum frequency margin above the 4GHz requirement.

Q7: Can I use MRF422 as a substitute?

A: No. MRF422 is a high-power RF transistor (150W, 20A) designed for power amplification in chassis-mount applications. It is not suitable for small-signal RF applications requiring the BFG35,115 specification. Package, power rating, and current handling are incompatible.

Q8: What inventory status should I consider for production planning?

A: BFR181WH6327XTSA1 has the highest inventory (275,300 pcs), followed by KST10MTF (391,101 pcs). However, KST10MTF is not frequency-compatible. For 4GHz-capable substitutes, BFP420FH6327XTSA1 (4,290 pcs) and BFP640FESDH6327XTSA1 (3,652 pcs) provide adequate supply for production requirements.

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