Blackfin ADSPbf506f Data Sheet: LFCSP Design and Manufacturing Guide

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本应用笔记（AN-772）详细介绍了Blackfin ADSPbf506f处理器的Blackfin数据手册，特别是关于其Lead Frame Chip Scale Package (LFCSP)的使用设计和制造指南。LFCSP是一种先进的芯片级封装技术，它结合了塑料封装、细线焊球和铜铅框架，提供了一种无引脚的封装形式，旨在优化小型化、高密度和热管理性能。 1. **简介**：该文档首先明确了应用笔记的目的，即为设计者和制造商提供针对LFCSP的全面指导，确保它符合JEDEC MO220和MO229标准，这表明在设计过程中必须遵循这些行业规范，以确保兼容性和互换性。 2. **包** **装描述**： LFCSP的特点是使用塑料封装，并通过外围输入/输出垫片与电路板连接。这些垫片位于封装的边缘，允许通过锡焊的方式建立电气连接。封装底部有一个暴露的热管理组件，即热导 paddles，以便高效地将热量从器件传递到印刷电路板，从而保持良好的热性能。 3. **设计与组装考虑**：本部分可能包括如何在设计阶段考虑封装尺寸、引脚布局、信号完整性以及电源和接地策略，确保电路板设计与LFCSP的特性相匹配。可能还会提到如何在电路板布局时考虑到封装的热膨胀系数，以防止热应力对系统造成影响。 4. **返修注意事项**：如果封装损坏或需要维修，文档可能会介绍如何安全地处理LFCSP的特殊性，如最小的拆卸区域、避免焊球断裂的风险以及重新焊接的技巧。 5. **电气特性**：提供了关于LFCSP内部元件的电气参数，如工作电压、电流规格、信号传输速度等，这对于理解处理器的电气性能至关重要。 6. **焊接可靠性**：这部分着重于讨论LFCSP的焊接工艺和要求，确保长时间稳定运行，可能包含建议的焊接温度范围、焊料类型和冷却时间等关键参数。 7. **参考文献**：最后，读者可以找到进一步的技术文档、标准和其他相关资源，以便深入研究和应用LFCSP技术。 AN-772 Blackfin ADSPbf506f的资料涵盖了LFCSP封装技术在实际应用中的各个方面，旨在帮助设计者和制造商实现高效、可靠和小型化的系统设计。通过遵循其中的指导，工程师可以充分利用Blackfin数据手册提供的信息，确保产品性能和生产过程的质量。

–4–

AN-772

The calculation for GD

MIN

does not account for the leads

on adjacent sides of the package. To avoid any solder

bridging between the two perpendicular leads on each

corner, a minimum clearance, C

, is needed. This clear-

ance is assumed as ≥ 0.1 mm and the value of GD

MIN

determined using the following constraint:

MIN

≥ AD

MAX

+ 2C

where:

MAX

= [(lead pitch) 3 (no. of leads on side

–1)] + pad width

The pad length is determined as follows:

Y = (ZD

MAX

– GD

MIN

)/2

To ensure a robust design and to minimize any possibility

of solder bridging during board assembly, a minimum

metal-to-metal clearance of 0.2 mm is required. There-

fore, a ﬁnal adjustment to the land pattern is made by

overlaying the package outline with the maximum metal

dimensions and adjusting the land pattern to maintain

0.2 mm minimum metal-to-metal clearance.

Thermal Paddle Design

The LFCSP is designed with an exposed thermal paddle

to conduct heat away from the package and into the

PCB. By incorporating thermal vias into the PCB thermal

paddle, heat is dissipated more effectively into the inner

metal layers of the PCB.

Depending upon the package paddle size, the PCB

thermal paddle size is modiﬁed to avoid solder bridg-

ing between paddle and the perimeter pads. This is

done by deﬁning a minimum clearance between the

outer edges of the thermal paddle and the inner edges

of the perimeter pads as C

. This minimum clearance is

ﬁxed at 0.25 mm to give the maximum size of the thermal

paddle as calculated by the following relationship:

D2’TH

MAX

= GD

MIN

– 2C

The number of thermal vias incorporated into the

design will depend on the power dissipation and

electrical requirements of the speciﬁc application.

There is a point of diminishing returns where ad-

ditional thermal vias may not signiﬁcantly improve the

performance of the package. This is shown in Figure 7

where the effect of number of vias on u

is plotted

for 7 mm 3 7 mm, 48-lead packages. A via diameter

of 0.3 mm is used for this simulation. As the via pitch

decreases, more vias can be incorporated for the

same thermal paddle size; however, the incremental

performance improvement reduces.

 (C/W)

# OF VIAS 4 9 16 36

MATRIX 22 33 44 66

PITCH (mm) 2.4 1.8 1.2 0.9

Figure 7. Effect of Number of Thermal Vias on

Package Thermal Performance

It is recommended that a via diameter of 0.3 mm

to 0.33 mm be used to set a pitch between 1.0 mm

and 1.2 mm. A representative of these arrays for a

7 mm 3 7 mm 48-lead LFCSP is shown in Figure 8.

THERMAL

VIA

THERMAL

PADDLE

Figure 8. PCB Thermal Paddle and Via



, 

(C/W)

0 50 100

SOLDER VOID (%)

Figure 9. Effect of Voids on Thermal Performance

In Figure 9, thermal performance u

is only marginally

affected by small multiple voids covering up to 50%

of the paddle area for a 6 mm 3 6 mm LFCSP. Note:

Small voids do not impact the reliability of the solder

joints; large voids in the thermal paddle area should be

avoided as these can affect electrical and mechanical

performance.

REV. 0

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