本文纯属翻译文档，来自the art of analog layout一书中的一章！
因为本人精力所限，未作修订，本文读起来会很生硬，或有错误，故附上原文
（英文），欢迎大家指正。
同时也希望大家把别的章节也翻译出来，聚少成多。
熔丝
熔丝是两个相连压点之间很短的连线部分，一般由最小线宽的铝条或多晶硅
构成。通过在两个相
连的压点间加大电流，进行编程或吹化处理，引起熔丝材料气化蒸发。编程以
后，熔丝变成一个开路电路。
图5.23A 显示了一个典型的铝熔丝例子，它除了包含一段很窄铝连线，没有
什么其他特别的结构。一个小的保护窗口（opening of protective overcoat）覆盖
在熔丝上，以使编程的过程中，蒸发的铝能从其挥发出去。这小窗口可能成为
污染物进入芯片的一个潜在通道，但如果省去它，蒸发的铝可能不能挥发出
去，当编程过后，有时导致熔丝重新形成。铝蒸汽的扩散也能使保护层破裂，
这破裂部分也允许铝蒸汽挥发，但他们有时会进入相邻的电路。大多数厂家同
意这种在钝化层（protective overcoat）上开小窗口的结构，以小的代价去防止
熔丝再生和鈍化层破裂。
Fuses
A fuse is simply a short section of minimum-width metal or polysilicon connected
between two bandpads. It is programmed or blown, by passing a large current
between the bondpads,causing the fuse material to vaporize.After programming the
fuse becomes an open circuit.
Figure 5.23A shows a typical example of a metal fuse, which consists of nothing
more than a constricted segment in a wide metal lead. A small opening in the
protective overcoat above the fuse allows the vaporized metal to escape during
programming. This opening represents a potential pathway for contaminants to enter
the die, but if it is omitted, the vaporized metal cannot escape and the fuse sometimes
reforms after programming. The explosive expansion of the metal vapor can also
crack the protective overcoat.These cracks allow the metal vapor to escape, but they
sometimes extent to adjacent circuitry. Most manufacturers agree that the inclusion of
an opening in the protective overcoat is a small price to pay to prevent fuse regrowth
and overcoat cracking.
FIGURE5.23 Layouts of (A) a typical metal fuse and (B) a polysilicon fuse.
图5.23B 显示的是一个典型的多晶硅熔丝。多晶硅被作为一个小电阻连接两
端的压点。像铝熔丝一样，为了不破坏钝化层，使多晶硅蒸汽挥发出去，需要
在钝化层上开一个小窗口。多晶硅熔丝的掺杂浓度要高，以便获得很低的电
阻，允许编程。熔丝的总阻值必须小于200Ω保证它能在10V的电压脉冲下编
程的可靠性。
Figure 5.23B shows a typical polysilicon fuse. The polysilicon is laid out as a small
resistor connecting two bondpads. As with the metal fuse, a small opening allows the
vaporized silicon to escape without rupturing the protective overcoat. The polysilicon
fuse must be heavily doped to obtain a sufficiently low resistance to allow
programming. The fuse must have a total resistance of no ore than 200Ω to ensure
reliable programming with a 10V pulse.
被用来对熔丝编程的压点不是标准的邦定压点，因此他们只要能保证有足够
的面积，使探针能可靠的扎在上面即可。为了和真正的邦定压点区分开来，这
些压点有时被叫做备用压点 。尽管他们的尺寸比标准的压点有所减小，但备用
压点仍占用了芯片很大的面积。有些工艺允许电路放置在备用压点下面，在这
种情况下，很少的面积被浪费。备用压点必须得放置在探针能够接触的位置。
通常都要求把他们放在芯片的外围。减少备用压点的个数能节省芯片面积，压
缩集成电路的成本。如果几个熔丝通过串联或并联优化组合，备用压点的数量
可能会减到最少。
The pads used to program fuses are not normally bonded, so they need only be large
enugh to allow the probe needles to reliably land on them. These pads are sometimes
called trimpads to distinguish them from true bondpads. Despite their reduced
dimensions, trimpads still require substantial die area. Some processes allow active
circuitry to reside underneath trim pads, in which case very little area is wasted. Trim
pads must be placed so that the probe needles can reach them; this usually requires
that they reside around the periphery of the die. Reducing the number of trimpads
saves die area and reduces the cost of the integrated circuit. The number of trimpads
required to blow the fuses can be minimized if several fuses are connected in series or
in parallel.
铝熔丝编程是容易的。铝熔化的可靠温度为660℃，但他的沸点高于2470
℃。在这时产生蒸发，大多数的铝已经熔化和容易喷射。在几毫秒内几百毫安
的脉冲将确保熔断熔丝。这喷射的铝往往会溅射到探针上，最后弄脏他们，可
能严重的情况会发生短路。探针卡要求进行特殊的清洗以便减少这个问题的发
生。与熔丝一体的难熔的滞留铝也能被可靠的编程；铝会被先溅射，而少量难
熔的铝很快也会被溅射。
Aluminum fuses are easy to program. Aluminum melts at a relatively low
tempreture (660℃)but boils at a much higher temperature (2470℃). By the time
vaporization begins,most of the metal is already molten and is readily ejected. A pulse
of several hundred milliamps for a period of a few milliseconds will reliably blow the
fuse. The ejected aluminum tends to splatter onto the probe needles and eventurally
fouls them so badly that shorts occur. The probe card may require occasional cleaning
to alleviate this problem. Metal fusses incorporating refractory barrier metal can also
be programmed reliably; the aluminum is ejected first, but the thin refractory metal
soon follows.
多晶硅熔丝编程是比较困难的。硅比铝需要更高的温度去熔化（1410℃ 比
660℃），而且当它迅速被加热的压力下，更容易碎裂。多晶硅可能破裂当它熔
化前，除非电流脉冲有一个极快的上升时间（<25nS）。如果不是这样，那么
多晶硅破裂将引起电流停止流动，阻止正确的编程。机械压力能使破裂的熔丝
随时重新形成。这种可靠性失效能被解决，通过提高加快编程脉冲的上升时间
使熔丝在破裂出现前就熔化，这是解决这种可靠性失效的有效办法。
Polysilicon fuses are more difficult to program.Silicon melts at a much higher
temperature than aluminum (1410℃ versus 660℃),and it is brittle and prone to
fracturing from the stresses of rapid heating. The polysilicon may crack before it
begins to melt unless the programming current pulse has an extremely fast rise time
(<25nS).Such fractures cause the current flow to stop and prevent proper
programming. Mechanical stresses can cause cracked fuses to reform at any time.
This type of reliability failure can be prevented by ensuring that the programming
pulse has a sufficiently fast rise time to blow the fuse before cracks appear.
当芯片封装后，多晶硅和铝熔丝编程都是很困难的。因为塑胶密封熔丝上的
窗口后，会阻止导电材被溅射出去，这些导电材料仍聚在熔寺附近，这样不仅
削弱了熔丝的熔化，而且也会易于他们重新形成。一些设计用电路去检测比较
已经编程和参考熔丝（未被编程的熔丝）的阻值，虽然这些电路是复杂的和不
实用的，但它允许封装后的电阻调整。现代的CMOS和BiCMOS电路设计为了
获得简单的编程电路和节省空间，有时会用EEPROM代替熔丝电路。
Both polysilicon and aluminum fuses are difficult to program after encapsulation. The
plastic seals the opening over the fuse and prevents the conductive material form
being ejected. Not only does this impair the blowing of the fuses, but it also makes
them prone to regrowth because conducive material remains near them. Some designs
use circuits to detect changes in resistance between a programmed fuse and a
reference fuse that is left unprogrammed. Although such circuitry is complex and
unwieldy, it does allow post-package trimming of resistors. Modern CMOS and
BiCMOS designs sometimes substitute electrically programmable read-only
memory(EEPROM) elements for the fuses to save space and to simplify the
programming circuitry.
编程处理能引起高地电压出现在电路与熔丝的连线上。熔丝在熔断前会有一
个瞬间的大电流流过，电流的突然中断会引起电压瞬变，这是由于寄生的自感
应的结果。这瞬变能导致二级管雪崩击穿或破坏栅氧层。最小化编程电路的回
路面积有助于减小瞬变的大小。特别糟糕的事是来自齐纳击穿效应。电路设计
者可以通过把熔丝放在受到冲击最小的电阻末端上，以减少编程瞬变带来的影
响。例如，常见的在NPN的发射极与地之间的Brokaw 带隙连接的电阻的调
整，它的修调应该放在电阻连地的端，以致这瞬变到达BE结以前，它从电阻
的其余部分流过。由于这最低的熔丝连接到地，这种连接也节省了一个修调压
点。
The programming process can cause high voltages to appear on circuitry connected to
the fuse. A large current flows through the fuse in the instant before it blows, and the
sudden interruption of this current can cause voltage transients due to parasitic
inductances. These transients can avalanche junctions or damage thin gate oxides. The
magnitude of the transients can be reduced by minimizing the loop area of the
programming circuit. Especially difficult cases may benefit from the addition of
integrated Zener clamps. Circuit designers can help minimize the impact of fuse
programming transients by placing the fuses on the least-vulnerable end of a resistor.
For example, the resistor normally trimmed in a Brokaw bandgap connects between
the emitter of an NPN transistor and ground. The trims should be placed on the
grounded end of the resistor so that transients must pass through the rest of the
resistor before reaching the base-emitter junction.This same connection also saves a
trimpad because the lowest fuse connects to ground.
几个熔丝可以组合成另外的修调方案。每段电阻应该设成权为2，这样有利于
保证所获得电阻在修调的范围内，获得均匀的值。这不仅能提供最大最精确的
修调范围，而且通过二进制算法，也简化了测试程序。权2能实现这两种方
法。如果一个电阻两端的电压要求修调，那么这些电阻应该串联，而且比例
为：2RIsb:4RIsb:8RIsb… 这里的RIsb为修调网络的最低位（LSB），图5.24A
显示了一个三位的权为 二的电压修调方案。如果要通过电阻来修调电流的话，
那么这些电阻应该被并联，并呈以下比例：Rmsb : Rmsb/2 : Rmsb/4 : Rmsb/8 …
这里的Rmsb表示这最高有效位（MSB）电阻（图5.24B）。
Several fuses in combination can provide additional trim resolution. The resistor
segments should be binary weighted to ensure that the achievable values of resistance
are uniformly spaced across the trim range. This not only provides the maximum
possible trim range for a given precision but also simplifies the design of the test
program by allowing the use of a binary search algorithm. Binary weighting can be
implemented in either of two ways. If the voltage across a resistor requires trimming.
Then the resistors should be connected in series and weighted RIsb:2RIsb:4 RIsb:8
RIsb …where RIsb is the value of the least significant bit (LSB) of the trim network,
Figure 5.24A shows a 3-bit binary-weighted voltage trim scheme. If the current
through a resistor requires trimming, then the resistors should be connected in parallel
and weighted in the ratio Rmsb : Rmsb/2 : Rmsb/4 : Rmsb/8 …where Rmsb is the
value of the most significant bit(MSB) resistor (Figure 5.24B).
FIGURE 5.24 Two different binary-weighted resistor trim schemes using fuse：
（A）
Series-connected an (B)parallel-connected.Both cases assume that the ground pad is
used to program the fuses.
一个精确的修调方案经常采用一个很小的LSB电阻。修调时最小的电阻小于
1kΩ时会过热，引起电阻变化，最糟糕的情况下，直接导致失效。较小的电阻
能采用并联两个或更多的电阻组合来实现。每一个组合有一个相对的大电阻，
但这种技术对于小于200Ω的许多电阻来说是不可行的。一种称作差分修调的
技术能实现小的LSB电阻。这个方案为每个修调单位有两个电阻，而不是一
个。这两个电阻采用并联形式，而熔丝被完整的保留着。熔断熔丝拆除其中一
个电阻，留另一个电阻独自流过电流。这有效的LSB电阻等于这两个电阻（熔
丝前后形成的电阻）的差值。图5.25中的例子显示了差分修调应用到一个两位
LSB、串联修调的方案。如果RA的值为1 kΩ，RB的值有250Ω,那么这电阻
并联的值就是200Ω，这 RB单独工作与两个并联电阻工作之间的差值为50
Ω，这50Ω小电阻，正是我们要修调的小电阻值。
A precision trim scheme often requires a very small LSB resistrance. Minimum-width
resistors of less than about 1kΩ may overheat during trimming, causing resistance
variations and, in extreme cases, outright failures. Smaller resistors can be
implemented as parallel combinations of two or more resistors, each having a
relatively large resistance, but this technique becomes impractical for resistors much
smaller than 200Ω. A technique called differential trimming can implement arbitrarily
small LSB resistances. This scheme requires two resistors per trim bit rather than one.
The two resistors are connected in parallel while the fuse remains intact. Blowing the
fuse disconnects one of the resistors and leaves the other to conduct the current alone.
The effective LSB resistance equals the difference between the two resistor values.
Figure 5.25 shows an example of differential trim applied to the LSB of a two-bit,
series-connected trim scheme. If RA has a value of 1 kΩ and RB has a value of
250Ω,then the parallel combination of these resistors equals 200Ω.The difference
between RB acting alone and the two resistors acting in parallel therefore equals 50Ω.
差分修调要求每个熔丝单元要两个修调压点，而标准的修调每个单元仅需一
个修调压点，这多出的一个修调压点使得(为了微调电阻的)差分修调法显得有
些不经济。但当电阻值小于500Ω时，采用它是比较好的，而对于大电阻的实
现，采用标准的修调比较好。
Differential trimming requires two trimpads per bit,while standard trimming requires
only one pad per bit.The additional trimmpads required for differential trim make this
technique uneconomic for all the smallest resistors. Resistors smaller than about
500Ωusually benefit from differential trimming,while larger resistors are better
implemented as standard trims.
熔丝修调方案要求修调压点分布在芯片的周边，但精确的电阻为了减小机械压
力往往放在芯片的内部。从芯片的边缘到内部的电阻，需要长的引线连到熔
丝。这些连线不仅浪费了芯片的面积而且也会接受来自其他电路的噪声。
Fuse trim schemes require trim pads around the periphery of the die,but precision
resistors normally reside in the interior to minimize mechanical stresses. Long leads
are required to connect fuses at the edge of the die to resistors in the middle.These
leads not only waste die area but can also pick up noise from other circuity. If CMOS
transistors are available, then these can be used as switches to reconfigure the resistor
network. These transistors can, in turn, be controlled by fuses placed around the
periphery of the die. Since the fuse leads no longer connect directly to the trim
resistors, they are less susceptible to noise, and their length and routing become less
critical. Care must be taken to ensure that the CMOS transistors have small on-
resistances compared with the trim resitors. The gate drive voltage for these
transistors must be derived from a well-regulated supply, since this voltage will
modulate their on-resistance. The design of remotely programmed trim networks is
beyond the scope of this text, but the foregoing comments should convey the general
concept.
Some designers have attempted to use remotely programmed poly fuses to implement
look-ahead trimming. A voltage sufficient to switch the transistor but inadequate to
blow the fuse can be used to test the results of programming the fuse before
committing to it. Unless the circuitry is specifically designed to switch at low voltages,
the look-ahead process may overstress the poly fuse, causing it to increase in value to
the point where it can no longer be reliably programmed.
Poly fuses have been reliably programmed after encapsulation by using circuitry to
compare the resistance of the blown fuse to an unprogrammed reference fuse.
Even if programming does not result in a clean open circuit, it almost invariable
causes resistance changes that can be detected in this manner.
